Eugene  W.Hilgard 


t>~-*---i 


ELEMENTARY    INSTRUCTION 


CHEMICAL    ANALYSIS. 

BY 

DR.  C.  REIIGIUS   FRESENIUS, 

CHEMICAL    ASSISTANT    IN    THE    LABORATORY    OF    THE 
UNIVERSITY    OF    GIESSEN. 

WITH 

A  PREFACE  BY  PROFESSOR  LIEBIG. 

EDITED     BY 

J.  LLOYD   BULLOCK, 

MEMBER    OF    THE  CHEMICAL    SOCIETY,    LATE    OF  THE    GIESSEN 
AND    PARIS   LABORATORIES. 


NE  W-YORK: 
D.  APPLETON  &  CO.,   200  BROADWAY. 

PHILADELPHIA  :    GEORGE    S.    APPLETON. 

M.DCCC.XLIV.  / 


1  I 


iS/H 


NEW- YORK: 

PRINTED  SY  HBNRY  LUDWIG,  72  VBSKY-BTRBET. 


PREFACE 

BY  PROFESSOR  IIEBIG. 


DR.  FRESENIUS  conducts  the  course  of  elementary  in- 
struction, in  mineral  analysis,  in  the  laboratory  of  the 
University  of  Giessen.  During  the  two  last  sessions  he 
has  followed  the  method  described  in  his  work,  entitled* 
"  Elementary  Instruction  in  Qualitative  Chemical  Analy- 
sis." This  method  I  can  confidently  recommend  from  my 
own  personal  experience  to  all  who  are  desirous  of  obtain- 
ing instruction  in  inorganic  analysis,  for  its  simplicity, 
usefulness,  and  the  facility  with  which  it  may  be  appre- 
hended. 

I  consider  Dr.  Fresenius'  work  extremely  useful  as  an 
introduction  to  Professor  H.  Rose's  excellent  manual,  and 
for  adoption  in  institutions  where  practical  chemistry  is 
taught,  but  it  is  especially  adapted  to  the  use  of  Pharma- 
ceutical Chemists. 

Further,  a  number  of  experiments  and  discoveries  have 
been  recently  made  in  our  laboratory,  which  have  enabled 
Dr.  Fresenius  to  give  many  new  and  simplified  methods  of 
separating  substances,  which  will  render  his  work  equally 
welcome  to  those  who  already  are  familiar  with  the  larger 
works  on  inorganic  analysis. 

JUSTUS    LIEBIG. 

415394 


EDITOR'S    PREFACE. 


THIS  work  of  Dr.  Fresenius  has  already  gone  through 
two  editions  in  Germany.  The  abundant  opportunities 
enjoyed  by  its  author  of  discovering  the  wants  felt  by  stu- 
dents in  entering  upon  the  practice  of  chemical  analysis^ 
and  his  position  in  the  school  at  Giessen,  has  enabled  him 
to  devise  a  method  of  study  of  the  highest  value.  That  it 
has  received  the  approbation  of  the  illustrious  HEAD  of  that 
school,  and  the  benefit  of  three  years'  practical  experience 
under  his  immediate  observation,  must  powerfully  recom- 
mend it  to  the  English  student  of  chemistry.  Whoever 
is  desirous  of  obtaining  the  knowledge  necessary  to  become 
a  practical  chemist,  will  be  in  no  small  degree  indebted  to 
Dr.  Fresenius  for  the  facilities  thus  afforded  him.  Every 
one  who  knows  any  thing  of  Giessen,  will  bear  testimony 
to  the  rigid  economy  of  time,  and  the  resolute  adoption  of 
every  improvement  in  method  which  characterise  that 
school,  and  serve  to  accomplish  the  many  chemists  annu- 
ally flocking-  there  for  the  completion  of  their  studies.  The 
author,  in  his  preface  to  the  first  edition,  tells  us  that  he 
was  led  to  compose  this  volume  upon  perceiving  that  the 
larger  works  on  chemical  analysis,  such  as  H.  Rose's, 
Duflos',  and  others,  although  admirable  in  themselves, 
present  great  difficulties  to  beginners,  which  difficulties 
may  be  summed  up  under  three  heads  J  1st,  Too  great 

* 


VI. 


copiousness  and  detail ;  2d,  The  absence  of  explanations 
of  the  causes  of  phenomena,  i.  e.  the  theory  of  the  opera- 
tions and  reactions  ;  and  3d,  The  omission  altogether  of 
many  substances  of  very  frequent  occurrence,  especially 
in  the  operations,  of  the  pharmaceutist,  such  as  the  or- 
ganic acids,  &c. 

In  avoiding  these  objections  to  former  works  on  chemical 
analysis,  Dr.  Fresenius,  I  think,  is  not  chargeable  with 
having  fallen  into  the  opposite  extreme  of  being  too  con- 
cise or  elementary. 

The  student  may,  perhaps,  at  first  be  disappointed  in 
taking  up  this  work,  to  find  that  there  are  no  tables  con- 
structed to  furnish  him  at  a  glance  with  all  he  is  desirous 
to  know  of  tests  and  reactions,  and  to  save  him,  as  he 
may  think,  trouble  and  time.  But  this  has  not  arisen 
from  oversight;  the  question  of  the  advantage  or  disad- 
vantage of  tables  to  the  student  has  been  fully  considered, 
and  the  author  has  decided- — and  the  decision  is  borne  out 
by  the  highest  authorities — that  such  tables  serve  no  really 
good  purpose  ;  they  rather,  on  the  contrary,  supply  but 
very  superficial  information,  and  satisfy  the  student  before 
they  have  really  informed  him.  The  information  contained 
in  this  work,  like  every  other  professing  to  teach  a  practical 
science,  requires  application  and  perseverance  to  attain ; 
but  if  begun  at  the  beginning,  if  the  student  will  carefully 
go  over  the  necessary  preliminary  facts,  the  examination 
of  his  tests,  and  the  reaction  of  the  simple  bodies  consecu- 
tively, and  make  himself  master  of  this  very  simple  and 
elementary  part  of  the  course,  he  will  find  few  or  no 
difficulties  when  entering  upon  the  more  elaborate,  and — 
what  might  appear,  without  this  preparation — complex  and 
intricate  processes  of  the  second  part,  the  analysis  of  corn- 


Vll. 

pound  bodies.  It  is  altogether  another  question  whether 
the  student  should  or  should  not  exercise  himself  and  his 
memory  by  tabulating  the  results  of  his  experiments  as  he 
proceeds  ;  and  to  this  question  we  reply  in  the  affirmative  : 
but  it  must  be  left  to  individuals  to  act  in  this,  according 
to  their  own  judgment,  and  their  own  feeling  of  its  ne.ces- 
sity. 

In  the  preface  to  the  Second  Edition,  Dr.  Fresenius  tells 
us  that  his  work  has  met  with  much  success,  having  been 
adopted  in  the  Pharmaceutical  Institution  of  Bonn,  &c., 
as  well  as  in  the  laboratory  of  Giessen  ;  and  that  he^  has 
improved  it  by  many  corrections  and  additions. 

For  my  own  part,  I  may  be  allowed  to  observe  that  the 
English  edition  was  undertaken  by  the  express  desire  of 
Professor  Liebig,  who  kindly  recommended  its  being  en- 
trusted to  my  care.  The  author  has  supplied  me  with 
many  corrections,  and  some  additions,  and  the  hope  is 
shared  by  us  in  common  that  it  will  facilitate  the  study  of 
analytical  chemistry  to  the  English  student,  and  in  every 
way  serve  to  promote  the  interests  of  the  science. 

J.  LLOYD  BULLOCK. 
22,  Conduit  Street,  Oct.  1,  1843. 


«*-  ^ 


INDEX, 


PART    I. 

INTRODUCTORY   COURSE  OF   QUALITATIVE  CHEMICAL 
ANALYSIS. 


Page 
PRELIMINARY  REMARKS. 

Definition,  design,  and  utility  of  qua- 
litative chemical  analysis,  and  con- 
ditions whereon  a  successful  study 
of  this  science  depends  .  •  13 

CHAPTER  I. 

Operations,  $  1       .  16 

1.  Solution,  $  2  ...  17 

2.  Crystallization,  $  3         .  19 

3.  Precipitation,  §4  .        .        .  20 

4.  Filtration,  §  5  ...  21 

5.  Decantation,  $  6  ...  22 

6.  Evaporation,  $  7  .  23 

7.  Distillation,  $8  ...  24 

8.  Roasting,  $9  ...  24 

9.  Sublimation,  $  10  ...  25 

10.  Smelting  and  fluxing,  $  11      .  25 

11.  The  use  of  the  blow-pipe,  §  12         26 

Appendix  to  Chapter  I. 
Apparatus  and  utensils,  $  13  .29 

CHAPTER  n. 

REAGENTS,  $  14  ...  31 

A.    Reagents  in  the  humid  way. 

I.  General  Reagents, 
a.  Reagents  principally  used  as  sim- 
ple solvents. 

1.  Water,  §  15  ...        34 

2.  Alcohol,  §  16          ...  35 

3.  Ether,  $  17         ....        35 
If.  Reagents  which  are   principally 

used  as  chemical  solvents. 

1.  Hydrochloric  acid  $18  .35 

2.  Nitric  acid,  §19               .  .           37 

3.  Nitro-muriatic  acid,  §  20  .37 

4.  Acetic  acid,  $  21             .  38 

5.  Muriate  of  ammonia,  $  22  .        39 
e.  Reagents  which  serve  especially  to 

separate  or  otherwise  to  charac- 
terize groups  of  substances. 


Pa 


1.  Reagent  papers,  $  23 

2.  Sulphuric  acid,  §  24      . 

3.  Sulphuretted  hydrogen,  $  25 

4.  Hydrosulphuret  of  ammonia, 
$26 

5.  Sulphuret  of  potassium,  $  27 

6.  Potash,  §  28         ... 

7.  Carbonate  of  potash,  $  29 

8.  Ammonia,  $30  . 

9.  Carbonate  of  ammonia,  $  31 

10.  Chloride  of  barium,  §  32 

11.  Nitrate  of  barytes,  §  33 

12.  Chloride  of  calcium,  $  34 

13.  Nitrate  of  silver,  $35 

14.  Perchloride  of  iron,  $  36 

II.  Special  reagents  in  the  humid  way 
a.  Reagents  which  serve  especially 
for  the  detection  or  separation  of 
individual  bases. 

1.  Sulphate  of  potash,  $  37 

2.  Phosphate  of  soda,  $  38 

3.  Neutral  chromate  of  potash,  $  39 


4.  Cyanide  of  potassium,  §  40      . 

5.  Ferrocyanide  of  potassium,  §  41 

6.  Ferricyanide  of  potassium,  $  42 

7.  Hydrofluosilicic  acid,  $  43 

8.  Oxalic  acid,  $44  .        . 

9.  Oxalate  of  ammonia,  §  45 

10.  Tartaric  acid,  §  46        .        . 

11.  Bitartrate  of  potash,  §  47 

12.  Acetate  of  barytes,  $  48 

13.  Caustic  barytes,  $  49 

14.  Protochloride  of  tin,  §  50      . 

15.  Chloride  of  gold,  $  51       . 

16.  Chloride  of  platinum,  $  52 

17.  Zinc,  $  53         .        ... 

18.  Iron,  $  54  ... 

19.  Copper,  $  55  ... 
b.  Special  reagents  which  are  parti- 
cularly employed  for  the  detec- 
tion and  separation  of  acids. 

1.  Acetate  of  potash,  $  56 

2.  Caustic  liine,  $  57 


54 

54 
55 
50 
57 

57 
58 
59 
GO 


INDEX. 


3.  Sulphate  of  lime,  $58  .  66 

4.  Chloride  of  magnesium,  $59  66 

5.  Protosulphateofiron,  $60       .  67 

6.  Solution  of  magnetic  oxide  of 

iron,  $  61  ...  67 

7.  Oxide  of  lead,  §62  '    .        .  68 

8.  Neutral  acetate  of  lead,  $  63  68 

9.  Basic  acetate  of  lead,  $  64        .  68 

10.  Hydrated  oxide  of  bismuth,  $  65  69 

11.  Sulphate  of  copper,  $66          .  70 

12.  Protonitrate  of  mercury,  $  67  70 

13.  Peroxide  of  mercury,  $  68        .  71 

14.  Perchloride  of  mercury,  $69  71 

15.  Ammonia-nitrate  of  silver,  $70  71 

16.  Sulphurous  acid,  $  71  .72 

17.  Chlorine,  $  72  .  72 

18.  Solution  of  indigo,  §73  .73 

19.  Starch  paste,  $  74         .        .  73 

B.    Reagents  in  the  dry  way. 
I.  Fluxes  and  means  of  decomposition. 

1.  Mixture  of  carbonate  of  soda 

and  carbonate  of  potash,  $  75  74 

2.  Carbonate  of  barytes,  §76         .  75 

3.  Nitrate  of  potash,  $  77  .  75 


n.  Slow  pipe  reagents. 
*.  Charcoal,  $  78  ... 

2.  Carbonate  of  soda,  $  79 

3.  Cyanide  of  potassium,  $  80 

4.  Biborate  of  soda,  $  81 

5.  Phosphate  of  soda  and  ammo- 

nia, $  82          .... 

6.  Protonitrate  of  cobalt,  §  83     . 


CHAPTER  ra. 

On  the  relation  of  the  various  sub- 
stances to  reagents,  §84        .      '  \ 

A.    Relation  of  the  metallic  oxides. 
First  group,  §  85 

a.  Potash  .... 

ft.  Soda        

e.  Ammonia 
Second  group,  §  86  .       •.       . 

a.  Barytes  .... 

b.  Strontian  .... 

c.  Lime  .... 

d.  Magnesia  .... 
Third  group,  §  87  ... 

a.  Alumina  .        .        •       *. 

b.  Oxide  of  chromium 

Fourth  group,  $  88  .       .       i 

a   Oxide  of  zinc        .  ;    . 

b.  Protoxide  of  manganese 

e.  Oxide  of  nickel 

d.  Protoxide  of  cobalt 

e.  Protoxide  of  iron 
/.  Peroxide  of  iron 

Fifth  group,  $  89  ... 


87 


First  section,  $  90         ...  107 

fl.  Oxide  of  silver         ...  107 

b.  Protoxide  of  mercury           .  108 

c.  Oxide  of  lead           ...  109 
Second  section,  $  91             .        .  Ill 

a.  Peroxide  of  mercury       .       .  Ill 

ft.  Oxide  of  copper            .       .  112 

c.  Oxide  of  bismuth             .        .  114 

d.  Oxide  of  cadmium       .       .  115 
Sixth  group,  $  92             ...  117 
First  class,  $  93             ...  117 

a.  Peroxide  of  gold              .        .  117 

ft.  Peroxide  of  platinum            .  118 

Second  class,  $  94  119 

a.  Oxide  of  antimony       .        .  119 

A.  Protoxide  of  tin        ...  122 

c.  Peroxide  of  tin      ...  124 

d.  Arsenious  acid         ...  126 

e.  Arsenic  acid          ...  134 
B.  Relations  of  the  acids  to  reagents, 

§  95 137 

I.  Inorganic  acids — First  group. 

First  section,  §96             ...  139 

a.  Arsenious  and  arsenic  acid  139 

ft.  Chromic  acid           ,        .        .  139 

Second  section,  §  97             .        .  141 

Sulphuric  acid          ...  141 

Third  section,  $  98        ...  142 

a.  Phosphoric  acid       ...  142 

b.  Boracic  acid          ...  144 

c.  Oxalic  acid                ...  145 

d.  Hydrofluoric  acid         .        .  146 
Fourth  section,  $  99         .        .        .  149 

a.  Carbonic  acid               .        .  149 

ft.  Silicic  acid               ...  150 

Second  group  of  inorganic  acids,  §  100  151 

a.  Hydrochloric  acid         .        .  152 

b.  Hydrobromic  acid            .        .  152 

c.  Hydriodic  acid              .       .  154 

d.  Hydrocianic  acid              .        .  155 
«.  Hydrosulphuric  acid             .  157 

Third  group  of  the  inorganic  acids, 

$  101 159 

a.  Nitric  acid            ...  159 

ft.  Chloric  acid             ...  160 

II.    Organic  Acids. 

First  group,  $  102             .        .        .  162 

a.  Oxalic  acid           ...  162 

b.  Tartaric  acid        *,.„  •     .       .  162 

c.  Paratartaric  acid           .       .  163 

d.  Citric  acid    .            ...  164 

e.  Malic  acid              .        .        .      .  166 
Second  group,  $  103         .        .        .  168 

a.  Succinic  acid        ...  J68 

ft.  Benzoic  acid             .        .        .  168 

Third  group,  §  104        .        .        .  170 

a.  Acetic  acid       ....  170 

b.  Formic  acid         ...  171 


! 


INDEX. 


XI. 


PART    II. 


SYSTEMATIC    COURSE    OF   QUALITATIVE    ANALYSIS. 


Preliminary  remarks  on  the  Course  of 
qualitative  analysis  in  general,  and 
on  the  plan  of  this  second  part 
in  particular  .  .  «i%.;* 

First  Section. 

PRACTICAL  PROCESS. 

I.  Preliminary  Examination,  $105 
j9.  The  body  under  examination  is 

solid          .     "  . 

1.  It  is  neither  a  pure  metal  nor  an 

alloy      .        .        .  V- 

2.  It  is  a  metal  or  an  alloy 

B.  The  substance  under  examination 
is  a  fluid        .... 

II.  Solution  of  bodies,  or  classifica- 

tion of  substances  according  to 
their  relations  to  certain  sot- 
vents,  §  106 

A.  The  substance  under  examination 

is  neither  a  metal  nor  an  alloy 

B.  The  substance  under  examination 

is  a  metal  or  an  alloy 

III.  Real  Examination. 

Compounds  supposed  to  consist  sim- 
ply of  one  base  and  one  acid,  or 
one  metal  and  one  metalloid. 

A.  Substances  soluble  in  water. 
Detection  of  the  base,  $  107 
Detection  of  the  acid. 

I.  Detection  of  inorganic  acids,  $  1 08 

II.  Detection  of  organic  acids,  §  109 

B.  Substances  insoluble,  or  sparing- 

ly soluble  in  water,  but  soluble 
in  hydrochloric  acid,  nitric 
acid,  or  aqua  regia. 

Detection  of  the  base,  I)  110     . 

Detection  of  the  acid. 

Detection  of  inorganic  acids,  $  111 

Detection  of  organic  acids,  <)  112 

C.  Substances  insoluble,  or  sparing- 

ly soluble  both  in  water  and 
acids. 

Detection  of  the  base  and  the  acid. 
§  113    . 


Page 


177 


181 
185 


180 


190 


192 

199 
201 


206 
208 


Compounds  in  which  all  the  more 
frequently  occurring  bases,  acids, 
metals  and  metalloids,  are  suppos- 
ed to  be  present. 

A.  Substances  both  soluble  and  inso- 
luble in  water,  and  soluble  in 
hydrochloric  acid,  or  nitric 
acid. 

Detection  of  the  bases,  $  114 
I.  The  solution  is  aqueous 
Detection  of  silver  and  protoxide 
of  mercury 


208 


210 
211 

212 


[I.  The  solution  is  hydrochloric     .       214 
[II.  The  solution  is  nitric    .        .        .    214 
Detection  of  silver        ...        214 
Precipitation  with  sulphuretted  hy- 
drogen, $  115  .        .        .        .214 
Treating  the  precipitated  metallic 
sulphurefs  with  hydrosulphuret 
of  ammonia          .        .        .        .216 
Detection  of  the  oxides  of  the  sixth 
group,    arsenic,   tin,    antimony, 
gold,  platinum,  $116        .        .       217 
Treating  the  metallic   sulphurets 
insoluble  in  hydrosulphuret  of 
ammonia,  with  nitric  acid,  $  117     221 
Detection  of  the  oxides  of  the  fifth 
group;    lead,  bismuth,  copper, 
cadmium,  peroxide  of  mercury       221 
Precipitation  with  hydrosulphuret 

of  ammonia,  $118         .  .    223 

Detection  of  the  oxides  of  the  third 
and  fourth  group,  &c. ;  alumina, 
oxide  of  chromium,  iron,  manga- 
nese, zinc,  cobalt,  nickel,  phos- 
phates, and  oxalates  of  the  alka- 
line earths,  §  118  .  .  .224 
Precipitations  with  carbonate  of 

ammonia,  $  119        .        .        .        230 
Detection  of  the  oxides  of  the  se- 
cond group;  barytes,  strontian, 
lime,  $119  .        .        .        .    231 

Magnesia,  $  120  ...        232 

Detection  of  the  oxides  of  the  fifth 

group,  $  121          ....    232 

Potash,  soda         ....        233 

Ammonia,  $  122     .        .        .        .234 

Detection  of  acids  and  metalloids      234 

A.  1.  Substances  soluble  in  water. 

I.  Absence  of  organic  acids,  $  123      .    234 

II.  Presence  of  organic  acids,  $  124         238 

A.  2.  Substances  insoluble  in  water 

but  soluble  in  hydrochloric  acid 

and  in  nitric  acid      .        .        .    242 

I.  Absence  of  organic  acids,  $  125          242 

II.  Presence  of  organic  acids,  $  126         243 

B.  Substances  insoluble,  or  sparingly 

soluble  both  in  water  and  in  hy- 
drochloric acid          .        .        .    244 

Detection  of  the  bases,  acids,  and 
metalloids,  $  127  .  .  .244 

Special  method  for  the  decomposi- 
tion of  insoluble  cyanides,  ferro- 
cyanides,  &c.,  §  128  .  .  251 

General  rules  for  the  detection  of 
inorganic  substances,  in  cases 
where  organic  substances  are 
present,  which  by  their  colour, 
consistence,  or  other  properties, 
impede  the  application  of  the 
reagents,  or  render  the  phenom- 
ena obscure,  $  129  .  .  .252 
IV.  Confirmatory  experiments,  $  130  254 


Xll. 

CHAPTER  IT. 

Explanatory  notes  and  additions  to 
the  practical  course 
I.  Remarks  on  the  preliminary  exa- 
mination     
II.  Additional  remarks  upon  solu- 
tion, &c  
in.    Additional  remarks  upon   the 
real    examination,    t)   107    to 
<S  129                  .... 

IN] 
Page 

254 
254 
255 

257 

257 
257 
201 

264 
264 
2G6 
267 

DEX. 

To  $117    .           .  *      . 
To  HIS 
To  «  127     . 
To  $128 

Appendix  to  Part  II. 

I.  General  scheme  for  a  judicious  ar- 
rangement of  the  succession  in 
which  substances  ought  to  be 
analyzed 
II.  Table  of  the  more  frequently  oc- 
curring forms  and  combinations 
of  the  substances  considered  in 
the  present  work,  with  especial 
regard  to  the  classes  to  which 
they  belong,  according  to  their 
various  degrees  of  solubility  in 
water,  &c. 

Page 
268 
270 
272 
273 

277 
280 

^.  General  survey  and  explanation 
of  the  analytical  course 
a.  Detection  of  the  bases 
b.  Detection  of  the  acids 
B.  Special   and  additional  remarks 
upon  the  systematic  course  of 
analysis 
To  4  114 
To  HIS     . 
To  $116 

ELEMENTARY   INSTRUCTION 


IN 


QUALITATIVE  CHEMICAL  ANALYSIS. 


PRELIMINARY  REMARKS, 

DEFINITION,      DESIGN,       AND     UTILITY      OF      QUALITATIVE! 

CHEMICAL     ANALYSTS,     AND    CONDITIONS    WHEREON    A 

SUCCESSFUL    STUDY    OF    THIS    SCIENCE    DEPENDS. 


CHEMISTRY  is  that  science  which  leaches  us  the  know- 
ledge of  the  elements  of  which  our  earth  consists,  their 
composition  and  decomposition,  and,  in  general,  their  re- 
lation to  each  other.  A  special  branch  of  this  science  is 
designated  by  the  name  of  analytical  chemistry,  inasmuch 
as  it  has  a  definite  object  in  view,  viz.,  the  analysis  of  com- 
pound bodies,  and  the  determination  of  their  constituent 
parts.  If  this  determination  of  the  constituent  parts  merely 
refers  to  their  nature,  the  analysis  is  called  qualitative; 
but  if  the  quantity  of  every  single  element  is  to  be  ascer- 
tained, the  analysis  is  called  quantitative.  The  object  of 
the  first,  therefore,  is  to  exhibit  the  constituent  parts  of  an 
unknown  substance  in  forms  already  known,  so  that  these 
new  forms  admit  of  safe  inferences  as  to  the  presence  of 
the  single  elements.  The  value  of  its  method  depends  on 
two  circumstances,  viz.  it  must  attain  the  object  in  view 
infallibly,  and  in  the  quickest  possible  manner.  Whereas, 
it  is  the  object  of  quantitative  analysis,  to  exhibit  those 
elements  rendered  manifest  by  qualitative  investigation,  in 
such  forms  as  admit  of  an  exact  determination  of  their 
amount. 
1 


14  PRELIMINAR       REMARKS. 


ways  'tod  '  rriearis  by"  which  these  various  objects 
are  attained,  differ,  of  course,  materially  from  each  other, 
The  study  of  qualitative  analysis  must,  therefore,  be 
separated  from  that  of  quantitative  analysis,  and,  as  a  mat- 
ter of  course,  must  precede  it. 

After  having  thus  generally  defined  the  meaning  and 
objects  of  qualitative  analysis,  we  must  now  shortly  con- 
sider, in  the  first  place,  the  preliminary  information  which 
qualifies  students  to  cultivate  this-  science  successfully,  the 
rank  which  it  occupies  in  the  department  of  chemistry,  the 
objects  to  which  it  extends,  the  advantages  derived  from 
it  ;  and,  in  the  second  place,  the  main  points  whereon  its 
study  is  based,  and  the  principal  branches  into  which  it  is 
distributed. 

In  order  to  enter  with  any  prospect  of  success  upon 
qualitative  experiments,  the  student  mast  previously  have 
acquired  some  knowledge  of  the  chemical  elements,  and  of 
their  most  important  combinations,  as  well  as  of  the  princi- 
ples of  chemistry  generally,  together  with  a  certain  readi- 
ness in  the  apprehension  of  chemical  processes.  This 
practical  art  demands,  moreover,  strict  order,  great  neat- 
ness, and  a  certain  degree  of  skill  in  manipulations.  If 
the  pupil  combines  with  these  qualifications  a  habit,  in  all 
cases  in  which  phenomena  contrary  to  experience  appear, 
of  imputing,  first  the  fault  to  himself,  or  rather  to  the  ab- 
sence of  some  condition  or  other  indispensable  to  the  suc- 
cess of  the  experiment,  —  and  a  firm  reliance  on  the  immu- 
tability of  the  laws  of  nature  cannot  fail  to  create  this  habit, 
—  he  possesses  every  requisite  to  render  his  study  of 
analytical  chemistry  successful. 

Now,  although  chemical  analysis  is  based  on  general 
chemistry,  and  cannot  be  cultivated  without  some  know- 
ledge of  the  latter,  yet/  on  the  other  hand,  we  must  con- 
sider it  also  as  a  kind  of  corner  stone,  upon  which  the  en- 
tire structure  of  this  science  rests  ;  for  it  is  almost  of  equal 
importance  for  all  branches  of  theoretical,  as  well  as  of 
practical  chemistry  ;  and  we  need  not  expatiate  here  on 
the  utility  and  advantages  which  the  physician,  the  apo- 
thecary, the  mineralogist,  the  rational  farmer,  the  artisan* 
and  many  others,  derive  from  it. 


PRELIMINARY   REMARKS.  15 

This  alone  would  be  a  sufficient  reason  to  recommend 
a  thorough  and  diligent  study  of  this  science,  if  even  its 
cultivation  possessed  none  of  those  attractions  which,  I 
may  safely  assert,  without  fear  of  contradiction,  it  must  of 
necessity  possess  for  every  one  who  devotes  himself  zeal- 
ously and  ardently  to  its  acquisition.  For  the  human 
mind  is  constantly  striving  for  the  attainment  of  truth  ;  it 
delights  in  the  solution  of  enigmas,  and  where  do  we  meet 
with  a  greater  variety  of  problems,  of  more  or  less  diffi- 
cult solution,  than  in  the  province  of  chemistry  ?  But  as 
a  problem,  an  enigma,  for  which,  after  long  pondering,  we 
can  find  no  solution,  wearies  and  discourages  th^mind  j 
so,  in  like  manner,  do  all  chemical  investigations,  if  the 
object  in  view  be  not  attained,  if  our  results  do  not  bear 
the  stamp  of  truth, — of  unquestionable  certainty.  A  half- 
knowledge  is  therefore,  in  every 'province  of  science,  but 
principally  here,  to  be  considered  worse  than  no  knowledge 
at  all,  and  the  student  must,  therefore,  be  especially  warn- 
ed against  a  mere  superficial  cultivation  of  chemical 
analysis* 

A  qualitative  experiment  may  be  made  with  a  twofold 
view,  viz.  either,  1st,  to  prove  that  some  definite  body  or 
other  is  or  is  not  contained  in  a  substance,  e.  g.  lead  in 
wine ;  or,  2d,  to  ascertain  all  the  constituents  of  a  chemi- 
cal combination  or  mixture.  Any  substance  whatever 
may,  of  course,  become  the  object  of  chemical  analysis. 

In  the  present  work,  however,  we  purpose  to  confine  our- 
selves to  those  elements  and  combinations  which  are 
employed  in  pharmacy,  arts,  and  trades,  and  understand 
thereby  the  following : 

I.   BASES'. 

Potash,  Soda,  Ammonia,  Barylgs,  Strontian,  Lime, 
Magnesia,  Alumina,  Oxide  of  Chromium,  Oxide  of  Zinc, 
Protoxide  of  Manganese,  Protoxide  of  Cobalt,  Oxide  of 
Nickel,  Protoxide  of  Iron,  Peroxide  of  Iron,  Oxide  of 
Cadmium,  Oxide  of  Lead,  Oxide  of  Bismuth,  Oxide 
of  Copper,  Oxide  of  Silver,  Protoxide  of  Mercury,  Pe- 
roxide of  Mercury,  Oxide  of  Platinum,  Oxide  of  Gold, 
Protoxide  of  Tin,  Peroxide  of  Tin,  Oxide  of  Anti- 
mony. 


16  OPERATIONS. 

II.  ACIDS. 

Sulphuric  Acid,  Nitric  Acid,  Phosphoric  Acid,  Ar- 
senious  Acid,  Arsenic  Acid,  Boracic  Acid,  Carbonic  Acid, 
Chromic  Acid,  Chloric  Acid,  Silicic  Acid,  Oxalic  Acid, 
Tartaric  Acid,  Paratartaric  Acid,  Citric  Acid,  Malic 
Acid,  Benzoic  Acid,  Succinic  Acid,  Acetic  Acid,  Formic 
Acid. 

III.  SALT-RADICALS,  AND  NON-METALLIC  SUBSTANCES. 

Chl&ine,  Iodine,  Bromine,  Cyanogen,  Fluorine,  Sul- 
phur, Carbon. 

The  study  of  qualitative  analysis  depends  principally 
on  four  points,  viz.  1st, "on  the  knowledge  of  operations ; 
2d,  on  that  of  reagents  and  of  their  application;  3d, 
on  that  of  the  relation  of  bodies  to  reagents  ;  and  4th,  on 
that  of  the  systematic  course  to  be  pursued  in  every  ex- 
periment. 

Chemical  analysis,  therefore,  requires  not  only  theoreti- 
cal knowledge,  but  also  practical  skill ;  and  it  is  obvious 
that  a  mere  speculative  study  of  it  can  no  more  lead  to 
success,  than  experimenting  at  random  ;  but  in  order  to 
obtain  satisfactory  results,  theory  and  practice  must  be 
combined. 


CHAPTER    I. 

OPERATIONS. 


THE  operations  of  analytical  and  synthetical  chemistry 
are  essentially  the  same,  modified  however  to  a  certain  ex- 
tent, according  to  the  object  we  have  in  view,  and  the 
quantities  upon  which  we  operate. 


SOLUTION.  17 

The  following  are  the  principal  operations  employed  in 
qualitative  investigations. 

§  2. 

1.     SOLUTION. 

The  general  meaning  of  "  solution"  is  "  the  combina- 
tion" of  a  gaseous,  liquid,  or  solid  substance,  with  a  fluid, 
forming  a  homogeneous  liquid.  But  we  call  the  solution 
more  properly  absorption  when  the  dissolved  substance  is 
gaseous  ;  and  when  liquid,  the  term  mixture  or  intermix- 
ture is  more  frequently  made  use  of.  The  term  solution, 
in  its  usual  and  more  restricted  sense,  is  confined  to  the 
perfect  union  of  a  solid  substance  with  a  fluid.  The 
more  minutely  we  divide  the  substance  to  be  dissolved, 
the  more  we  facilitate  its  solution.  The  liquid,  by  means 
of  which  the  solution  is  effected,  is  called  the  solvent.  We 
call  the  solution  chemical,  if  this  solvent  forms  a  chemical 
combination  with  the  substance  dissolved  ;  simple,  if  no 
definite  combination  takes  place. 

A  simple  solution  contains  the  dissolved  body  in  a  free 
and  unconnected  state,  and  with  all  its  original  properties, 
except  those  dependent  on  its  form  and  cohesion  ;  and 
when  it  separates  from  the  solvent  in  the  same  unaltered 
state,  as  soon  as  the  latter  is  withdrawn.  Common  salt 
dissolved  in  water  is  a  familiar  instance  of  a  simple  solu- 
tion. The  salt  here  imparts  its  peculiar  taste  to  the  water, 
and  on  evaporating  the  latter,  we  re-obtain  common  salt  in 
its  original  form.  A  simple  solution  is  called  saturated 
when  the  solvent  has  received  as  much  as  it  can  hold  of 
the  substance  to  be  dissolved.  But  as  fluids,  on  an  aver- 
age, dissolve  larger  quantities  of  a  substance,  the  higher 
their  temperature,  the  term  saturated  can  only  refer  to  a 
certain  temperature ;  and  it  must  be  considered  a  rule,  that 
elevation  of  temperature  facilitates  and  accelerates  simple 
solution. 

A  chemical  solution  contains  the  substance  dissolved, 
not  in  the  same  state  nor  with  the  same  properties  as  be- 
fore ;  the  dissolved  body  is  no  longer  free,  but  intimately 
combined  with  the  solvent,  which  latter  has  likewise  lost 
its  original  properties  ;  the  result  of  this  combination  has 


18  SOLUTION. 

been  the  formation  of  a  new  body,  the  solution,  therefore, 
now  manifests  the  properties  of  this  newly-formed  sub- 
stance. A  chemical  solution,  too,  may  certainly  be  ac- 
celerated by  elevation  of  temperature,  and  this  is  indeed 
usually  the  case,  as  heat  generally  promotes  the  action  of 
bodies  upon  each  other.  But  the  quantity  of  the  dissolved 
body  remains  always  the  same,  in  proportion  to  a  given 
quantity  of  the  solvent,  whatever  may  be  the  difference  of 
temperature  ;  their  combining  proportions  are  invariable, 
and  independent  of  the  gradations  of  temperature. 

In  chemical  solution,  the  solvent  and  the  body,  on  which 
it  acts,  have  always  opposite  properties,  and  their  tendency 
is  mutually  to  neutralize  these  opposite  properties.  Fur- 
ther, solution  ceases  as  soon  as  this  tendency  is  satisfied  ; 
if  we  add  more  of  the  solid  body  it  remains  unaltered. 
The  solution  in  this  case  also  is  called  saturated,  or  more 
properly  neutralized^  and  the  point  which  denotes  it  to  be 
completely  so,  is  called  the  point  of  saturation  or  neutrali- 
zation. The  substances  by  means  of  which  chemical  so- 
lutions are  effected,  are,  in  most  cases,  either  acids  or 
alkalies.  They  all  require,  first,  a  simple  solvent  to  be 
converted  to  the  fluid  state.  When  the  opposite  properties 
of  acid  and  base  have  mutually  neutralized  each  other, 
and  the  new  combination  has  been  formed,  the  real  con- 
version into  fluid  form  takes  place,  only,  if  the  product  of 
this  new  combination  possesses  the  property  of  forming  a 
simple  solution  with  the  liquid  present:  e.  g.  when  an 
aqueous  solution  of  acetic  acid  is  brought  into  contact 
with  oxide  of  lead,  there  ensues,  first,  a  chemical  combina- 
tion of  the  acid  with  the  oxide,  and  then  a  simple  solution 
of  the  thereby  produced  acetate  of  lead,  in  the  water  of  the 
menstruum. 

Crystallization  and  precipitation  are  the  reverse  of  so- 
lution, as  they  have  for  their  object  the  conversion  of  a 
fluid  or  dissolved  substance  into  the  solid  state.  As  both 
depend  on  the  same  cause,  viz.  on  the  absence  of  a  sol- 
vent, it  is  impossible  to  assign  exact  limits  to  either,  and 
in  many  cases  they  merge  into  each  other.  We  must, 
however,  consider  them  separately,  since  they  essentially 
differ,  as  well  in  their  extreme  forms,  as,  in  most  cases, 


CRYSTALLIZATION.  19 

in  the  special  objects  we  purpose  to  attain  by  their  appli- 
cation. 

5  3. 

%.   CRYSTALLIZATION. 

We  understand  by  the  term  crystallization,  in  a  more 
general  sense,  every  operation,  every  process  in  which 
bodies  pass  from  a  fluid  to  a  solid  state,  assuming  certain 
regular,  determinate,  geometrical  figures.  But,  as  these 
figures,  which  we  call  c^stals,  are  the  more  regular,  and 
consequently  the  more  perfect,  the  more  slowly  the  opera- 
tion is  carried  on,  we  always  connect  with  the  term  "  crys- 
tallization," the  accessary  idea  of  a  slow  separation, — of  a 
gradual  conversion  to  the  solid  state.  The  formation  of 
crystals  depends  on  the  regular  arrangement  of  atoms  ;  it 
can  only  take  place  if  these  atoms  possess  perfect  free- 
dom of  motion,  and  thus,  generally,  only  when  a  substance, 
from  the  fluid  or  gaseous,  changes  to  the  solid  state. 
Those  cases,  in  which  it  is  sufficient  merely  to  heat  or  to 
soften  a  solid  body,  to  induce  crystallization,  must  be  con- 
sidered as  exceptions, — as,  e.  g.  barley-sugar  becoming 
white  and  opaque,  or  crystallizing,  when  moistened. 

To  induce  crystallization  we  must  remove  the  causes  of 
the  fluid  or  gaseous  form  of  a  substance.  These  causes, 
.are  either — heat  alone,  e.  g.  in  metals  in  fusion,  or  sol- 
vents alone,  as  in  an  aqueous  solution  of  common  salt ; 
or  both  combined,  as  in  a  hot  and  saturated  aqueous  solu- 
tion of  nitre.  In  the  first  instance,  we  can  obtain  crys- 
tals only  by  cooling  the  substance  we  wish  to  crystallize; 
in  the  second,  only  by  evaporating  the  menstruum  ;  and  in 
the  third,  by  either  of  these  means.  The  most  frequently 
occurring  cases  of  crystallization  are  those  by  means  of 
cooling  hot  ard  saturated  solutions.  The  liquors  which  re- 
main after  the  separation  of  the  crystals,  are  called  mother 
waters.  The  term,  amorphous  bodies,  is  applied  to  such 
soli'l  substances  as  have  no  crystalline  form. 

We  cause  crystallization  to  take  place,  generally,  either 
to  obtain  the  substance  crystallized  in  a  solid  form,  or  to 
separate  it  from  other  substances  dissolved  in  the  same 
menstruum. 


20 


§4. 

3.    PRECIPITATION. 

This  operation  differs  from  crystallization  inasmuch  as 
in  precipitation  the  substance  dissolved  is  converted  to  the 
solid  state,  not  in  a  slow  and  gradual  manner,  but  sud- 
denly ;  it  is  a  matter  of  perfect  indifference,  as  regards  the 
application  of  the  term  precipitation  to  the  process,  whether 
this  substance  is  crystalline  or  amorphous  j  whether  it 
gravitates  to  the  bottom  of  the  vessel,  or  whether  it  as- 
cends or  remains  suspended  in  the  liquid.  We  may  cause 
precipitation  to  take  place,  either,  1st,  by  modifying  the 
solvent ; — thus  sulphate  of  lime  (gypsum)  separates  im- 
mediately from  its  solution  in  water,  if  this  watery  by  the 
addition  of  alcohol,  is  converted  into  diluted  alcohol ;  or 
2d,  By  separating  some  substance  insoluble  in  the  men- 
*g|ruumVj — thus,  if  ammonia  be  added  to  a  solution  .of  sul- 
pf&te  of  alumina,  the  composition  of  this  latter  salt  takes 
placfe  and  alumina,  not  being  soluble  in  water,  is  precipi- 
tated.^ Precipitation  takes  place  also  when,  by  the  action 
of  single  or  compound  chemical  affinity,  new  combina- 
tions ejisue  which  are  insoluble  in  the  menstruum ;  thus 
ox1ftateyQ£lime  precipitates  on  adding  oxalic  acid  to  a  solu- 
tion pf  acetate  of  lime  ;  chromate  of  lead  on  mixing,  chro- 
maje  of  potash  with  nitrate  of  lead.  In  decompositions  of 
/this  kind,  induced  by  simple  or  compound  affinity,  one  of 
the  new  combinations  generally  remains  in  solution,  and 
the  same  is  sometimes  the  case  with  the  substance  separ- 
ated,— thus  in  the  instances  just  mentioned,  the  sulphate 
of  ammonia,  the  acetic  acid,  and  the  nitrate  of  potash,  re- 
main in  solution.  Cases  may,  however,  happen,  where 
both  products  precipitate,  so  that  nothing  remains  in  solu- 
tion, e.  g.  when  a  solution  of  sulphate  of  magnesia  is  mix- 
ed with  water  of  barytes ;  or  a  solution  of  sulphate  of 
silver  with  chloride  of  barium. 

Precipitation  is  applied  to  the  same  purposes  as  crys- 
tallization: either,  1st,  to  obtain  a  substance  in  a  solid 
form ;  or  2d,  to  separate  it  from  other  substances  dis- 
solved in  the  same  menstruum.  But  in  qualitative  analysis 
we  employ  this  operation  especially,  in  order  to  detect 


FILTRATION.  21 

substances  by  the  colour,  and  the  properties  and  relations 
in  general,  which  they  exhibit  when  precipitated,  either 
alone  or  in  combination  with  other  substances.  The  solid 
body  separated  by  this  process,  is  called  precipitate,  and 
the  substance,  which  is  the  immediate  cause  ot  this  sepa- 
ration, is  termed  the  precipitant.  For  the  sake  of  a  more 
particular  designation,  we  apply  various  terms  to  precipi- 
tates, according  to  their  different  nature  ;  thus  we  distin- 
guish crystalline,  pulverulent,  flocculent,  curdy,  gelatinous 
precipitates,  &c.  &c. 

The  term  turbid  is  made  use  of,  when  a  precipitate  is 
in  a  state  of  such  minute  division,  and  so  small  in  quan- 
tity, that  its  particles  cannot  be  clearly  distinguished,  and 
that  the  fluid  in  which  it  is  suspended  merely  appears 
troubled.  We  may  generally  promote  the  separation  of  a 
precipitate  by  strongly  agitating  the  menstruum,  as  well 
as  elevating  its  temperature.  The  vessels  used  for  the 
purpose  of  precipitation,  must,  therefore,  admit  of  either 
of  these  operations.  In  qualitative  analysis  we  principally 
make  use  of  tubes  of  thin  glass,  closed  at  the  bottom,  such 
as  are  usually  called  test-tubes,  or  test-cylinders.  Beside 
the  advantages  just  mentioned,  they  permit  the  experi- 
mentalist closely  to  inspect  the  whole  process,  as  well  as 
the  colour  of  the  liquids  and  precipitates,  and  to  experi- 
mentalize with  very  small  quantities. 

Two  different  operations,  according  to  circumstances, 
are  employed  in  analysis,  in  order  mechanically  to  sepa- 
rate a  fluid  from  matter  suspended  therein,  namely,  "Jil- 
tration"  and  " decantation" 

§  5. 

4.    FILTRATION. 

We  purify  liquids,  by  means  of  this  operation,  in  pour- 
ing the  fluid  from  which  we  wish  to  remove  the  mechani- 
cally-suspended solid  particles,  on  a  filter,  for  which 
purpose  we  usually  employ  unsized  paper,  supported  by 
a  funnel ;  for  an  apparatus  of  this  description  allows  the 
liquid  to  trickle  through  with  ease  ;  and,  on  the  other  hand, 
completely  retains  the  solid  particles.  We  use  smooth 


22  DECANTATION. 

filters  and  plaited  filters  :  the  former,  in  such  cases  where 
the  defiltrated  solid  substance  is  to  be  made  use  of ;  the 
latter,  when  we  merely  wish  to  clear  the  solution.  Smooth 
filteis  are  produced  by  folding  a  circular  paper  doubly  to- 
gether, so  that  the  folds  form  right  angles.  The  prepara- 
tion of  plaited  filters  is  more  properly  a  matter  for  ocular 
demonstration  than  for  description,  In  minute  operations, 
care  should  be  taken  that  the  filters  do  not  reach  over  the 
brim  of  the  funnel.  It  is  in  most  cases  advisable  to  moisten 
the  filter  previous  to  use,  because  then,  not  only  the  filtra- 
tion proceeds  more  rapidly,  but  the  solid  particles  of  the 
substances  to  be  filtered  are  less  liable  to  pass  through  the 
pores  of  the  filter.  The  paper  selected  for  the  purpose  of 
filtration,  must  be  as  free  as  possible  from  inorganic  sub- 
stances, especially  iron  and  lime.  It  is  advisable  to  have 
always  two  sorts  on  hand,  one  of  greater  density  for  the 
separation  of  very  minute  precipitates,  and  one  of  greater 
porosity  for  the  speedy  separation  of  grosser  particles. 
The  funnels  must  be  either  of  glass  or  of  porcelain. 

§  6. 

5.   DECANTATION. 

This  operation  is  frequently  made  use  of  instead  of  fil- 
tration, if  the  solid  particles  to  be  removed  are  of  consider- 
ably greater  specific  gravity  than  the  liquid  in  which  they 
are  suspended.  They  in  such  cases  speedily  gravitate  to 
the  bottom,  and  are  deposited  there,  so  that  it  becomes 
easy,  either  to  decant  the  supernatant  liquid  by  sim- 
ply inclining  the  vessel,  or  to  remove  it  by  means  of  a 
syphon. 

In  such  cases  where  we  employ  these  operations  (filtra- 
tion or  decantation)  in  order  to  obtain  the  solid  substance 
out  of  the  liquid  in  which  it  is  suspended,  we  must  after- 
wards free  this  substance  by  repeated  washing  or  rinsing 
from  the  liquid  still  adhering  to  it.  This  operation  is 
termed  edulcoration  or  rinsing.  In  order  to  edulcorate  a 
precipitate  collected  on  a  filter,  we  most  frequently  make 
use  of  the  syringe  bottle, — a  glass  vessel,  stopped  with  a 
perforated  cork,  into  which  a  small  glass  tube  is  adapted, 


EVAPORATION,  23 

drawn  out  at  the  top  into  a  fine  point.  If  air  be  blown 
through  this  tube,  into  the  flask,  and,  when  the  air  is  suffi- 
ciently compressed^  the  flask  be  reversed,  so  that  the  inner 
aperture  of  the  tube  comes  under  water,  a  minute  stream 
of  water  is  expelled,  peculiarly  adapted  to  the  rinsing  of 
precipitates. 

There  are  four  operations  by  means  of  which  we  sepa- 
rate volatile  substances  from  less  volatile  or  from  fixed 
bodies,  viz,  EVAPORATION,  DISTILLATION,  ROASTING,  and 
SUBLIMATION.  The  two  former  of  these  operations  always 
refer  to  fluids,  the  two  latter  only  to  solid*. 

§  7. 

6.    EVAPORATION, 

This  is  one  of  the  most  frequently-employed  operations. 
We  have  recourse  to  it  when  a  volatile  fluid  is  to  be  sepa- 
rated from  another  less  volatile,  or  from  a  fixed  substance, 
(either  fluid  or  solid,)  if  by  this  separation  we  only  intend 
to  obtain  this  residuary  substance,  without  heeding  the 
evaporating  substance.  Thus,  evaporation  serves,  for  in- 
stance, to  remove  from  a  saline  solution  part  of  its  water, 
in  order  to  induce  the  salt  to  crystallize,  or,  also,  to  re- 
move all  the  water  from  the  solution  of  an  uncrystallizable 
substance,  so  as  to  obtain  this  latter  in  a  solid  form,  &c.  &c. 
The  evaporating  water  is  entirely  disregarded,  in  either  of 
these  cases,  and  the  only  object  in  view  is  to  obtain  in  the 
former  case  a  more  concentrated  fluid,  and,  in  the  latter, 
a  dry  substance.  These  objects '  are  always  attained  by 
converting  the  fluid  to  be  removed,  into  the  gaseous  state  j 
in  ordinary  cases,  therefore,  by  exposing  it  to  heat ;  some- 
times, also,  by  leaving  the  fluid  for  a  certain  time,  in  con- 
tact with  the  atmosphere,  or  in  confined  air,  constantly  kept 
dry  by  hygroscopic  substances  ;  or,  in  many  cases,  by 
placing  the  fluid  in  a  rarified  air,  with  the  simultaneous 
application  of  hygroscopic  substances.  The  heating  pro- 
cess is  conducted  either  over  a  free  fire,  (coal-fire  or  flame 
of  spirits  of  wine,)  or  in  the  sand-bath,  or  by  means  of 
steam,  (in  the  water-bath,)  &c.  &c.  Concentrated  sul- 
phuric acid  and  slaked  lime,  and  also  chloride  of  calcium, 


24  DISTILLATION.       ROASTING. 

are  used  as  the  cheapest  and  most  efficient  hygroscopic 
substances.  The  vessels  used  in  evaporation  are  of  por- 
celain, glass,  platinum,  or  silver,  and  have  usually  the 
shape  of  a  shallow  basin. 

§  8. 

7.   DISTILLATION* 

This  operation  has  for  its  object  the  separation  of  a  vol- 
atile liquid  from  a  less  volatile  or  fixed  substance,  either 
solid  or  fluid,  and  the  recovery  of  the  evaporating  fluid, 
In  order  to  attain  this  object,  it  is  necessary  to  reconvert 
the  liquid  from  the  gaseous  form  in  which  it  evaporated, 
into  the  fluid  state.  A  distilling  apparatusr  therefore,  con- 
sists of  three  parts,  whether  separated  from  each  other  or 
not,  is  quite  indifferent.  These  three  parts  are, — 1st,  a 
vessel  in  which  the  liquid  to  be  distilled  is  heated,  and 
thus  converted  into  vapour ,'  2d,  an  apparatus  in  which 
this  vapour  is  cooled  again  or  condensed,  and  thus  recon- 
verted to  the  fluid  state  ;  and  3d,  a  vessel  which  receives 
the  distilled  fluid.  In  distillation  on  a  small  scale,  we 
generally  employ  small  glass  retorts  and  receivers,  but  in 
the  distillation  of  large  quantities,  either  a  metallic  appa- 
ratus,— a  copper  still  with  helmet,  and  condensing  tube  of 
pewter,  or  large  glass  retorts. 

§  9. 

8.  ROASTING* 

Roasting  is,  in  a  certain  measure,  for  solid  bodies,  what 
evaporation  is  for  fluids  ;  for  the  object  to  which  we  ap- 
ply it  is,  (at  least  generally,)  the  separation  of  a  volatile 
substance  from  a  less  volatile,  or  from  a  fixed  body,  mere- 
ly for  the  purpose  of  purifying  this  latter  residuary  sub- 
stance. Roasting  always  presupposes  the  application  of 
a  high  temperature,  and  in  this  it  differs  from  exsicca- 
tion. The  form  or  state  which  the  volatilized  substance  as- 
sumes on  cooling,  is  a  matter  of  perfect  indifference  as  to 
the  name  of  the  operation* 

This  is  the  usual  design  in  the  application  of  roasting. 
Jn  some  instances,  however,  substances  are  heated  merely 


SUBLIMATION.       SMELTING    AND    FLUXING*  25 

for  the  purpose  of  modifying  their  state,  without  any  vola- 
tilization taking  place  ;  e.  g.  in  the  conversion  of  oxide  of 
chromium  into  its  insoluble  modification,  &c,  &c.  Cruci- 
bles are  the  vessels  made  use  of  in  roasting.  In  analytical 
experiments  we  select,  according  to  the  substances  to  be 
heated,  either  porcelain,  or  platinum,  or  silver  crucibles. 
In  operations  on  a  large  scale,  wa  employ  either  hessian 
or  black-lead  crucibles.  The  necessary  heat  we  obtain 
either  from  a  coal-fire,  or  in  experiments  on  a  small  scale, 
most  usually  by  means  of  a  Berzelius  spirit-lamp. 

§  10. 

*  • .  • 

9.    SUBLIMATION 

Is  that  operation,  whereby  solid  bodies  are  converted  in- 
to vapours  by  the  application  of  heat,  and  condensed  again 
by  cooling,  to  a  solid  state ;  the  substance  thus  volatilized 
and  recondensed  is  called  a  sublimate.  Sublimation  is 
consequently  a  distillation  of  solid  bodies.  We  generally 
employ  this  process  for  the  separation  of  substances  of 
different  degrees  of  volatility.  Its  application  is  of  the 
highest  importance  in  analysis,  for  the  detection  of  divers 
substances,  e.  g,  of  arsenic.  The  vessels  used  in  sublima- 
tion are  of  various  shapes,  according  to  the  different  de- 
grees of  volatility  of  the  substance  we  have  to  operate  upon. 
In  sublimation  for  analytical  purposes  we  generally  em- 
ploy glass  tubes  closed  at  both  ends. 

§  11. 

10.   SMELTING    AND  FLUXING. 

We  designate  by  the  term  "  smelting,"  the  conversion 
of  a  solid  substance  into  a  fluid  form,  by  the  application  of 
heat,  and  apply  this  operation  generally  to  the  purpose 
either  of  combination  or  of  decomposition  of  bodies.  The 
term  "  fluxing"  is  applied  to  this  process  in  such  cases 
where  a  substance,  either  insoluble  or  difficult  of  solution 
in  water  and  acids,  is,  by  being  fused  with  some  other  body, 
modified  or  decomposed  in  such  a  manner,  that  the  former 
or  its  new-formed  combinations,  afterwards  admit  of  solu- 
tion in  water  or  acids.  We  employ  in  analysis,  according 


26  USE    OF   THE    BLOW-PIPE. 

to  circumstances,  either  porcelain,  silver,  or  platina  cruci- 
bles, for  the  purposes  of  these  operations.  It  we  are  una- 
ble to  produce  the  necessary  degree  of  heat  by  means  of  a 
Berzelius  spirit-lamp,  the  crucible  containing  the  substance 
or  substances  to  be  fused,  may  be  placed  in  a  larger,  hes- 
sian  crucible,  and  this  latter  exposed  to  a  charcoal  or  coke 
fire. 

The  application  of  fluxing  is  especially  required  in  the 
analysis  of  the  sulphates  of  alkaline  earths,  and  of  many 
silicates.  The  flux  most  commonly  used  is  carbonate  of 
soda,  or  carbonate  of  potash,  or,  better  still,  a  mixture  of 
both,  in  equal  atomic  proportions,  (vide  §  75.)  In  cer- 
tain cases,  carbonate  of  barytes  is  used  instead  of  carbon- 
ate of  soda  or  potash,  (vide  §  76.)  But  in  either  case 
the  operation  is  conducted  in  platina  crucibles. 

We  will  here  briefly  lay  down  a  few  precautionary  rules 
for  the  prevention  of  damage  to  the  platinum  vessels  used 
in  these  operations.  No  substance,  evolving  chlorine, 
ought  to  be  treated  in  platinum  vessels  ;  no  nitrate  of  pot- 
ash, caustic  potash,  metals,  sulphur  or  sulphurets,  should 
be  fused  in  such  vessels,  nor  ought  easily  deoxidizable 
metallic  oxides,  organic  metallic  salts,  and  phosphoric  salts, 
to  be  heated  therein  when  organic  compounds  are  present. 
It  is  also  detrimental  to  platinum  crucibles  ;  and  especially 
to  their  covers,  to  expose  them  directly  to  a  strong  coal- 
fire,  (i  e.  without  shielding  them  in  larger,  hessian  cruci- 
bles,) because  siHcide  of  platinum  is  easily  formed,  in  such 
cases,  by  the  influence  of  the  ashes,  and  this  renders  the 
vessels  brittle* 

§  12. 

11.   THE    USE    OF    THE    BLOW-PIPE. 

The  application  of  the  blow-pipe  is  of  the  utmost  im- 
portance in  analytical  chemistry*  We  have  here  to  con- 
sider, first,  the  necessary  apparatus  ;  then,  the  manner  of 
its  application;  and,  lastly,  the  results  of  the  operation. 

A  blow-pipe  is  a  small  instrument,  usually  made  of  brass. 
It  was  originally  used  by  metallurgists  for  the  purpose  of 
soldering,  whence  it  derived  the  name  of  soldering-pipe. 
It  consists  of  three  distinct  parts  :  viz.  1st,  a  tube  through 
which  air  is  blown  from  the  mouth ;  2d,  a  small  vessel 


USE    OF    THE    BLOW-PIPE.  27 

into  which  this  tube  is  ground  air-tight ;  this  vessel  serves 
to  collect  and  retain  the  moisture  of  the  air  blown  into  the 
tube  ;  and  3d,  a  smaller  tube,  also  closely  fitted  into  this 
vessel,  forming  a  right  angle  with  the  large  tube,  and  hav- 
ing a  very  fine  aperture  at  its  anterior  extremity.  The 
blow-pipe  serves  to  conduct  a  fine  and  continuous  stream 
of  air  into  the  flame  of  a  candle  or  lamp.  Such  a  flame, 
under  ordinary  circumstances,  presents  to  the  eye  three 
distinct  parts  ;  viz.  1  st,  a  dark  nucleus  in  the  centre  ;  2d, 
a  luminous  part  surrounding  this  nucleus  ;  and  3d,  a  kind 
of  mantle  encircling  the  whole  flame,  and  but  feebly  lu- 
minous. The  dark  nucleus  is  formed  by  the  gases  which 
the  heat  evolves  from  the  fuel ;  these  gases  cannot  burn, 
from  want  of  oxygen.  In  the  luminoussphere  they  come 
into  contact  with  a  certain  quantity  of  oxygen,  although  in- 
sufficient for  their  complete  combustion.  The  hydrogen 
of  the  carburetted  hydrogen  gases  evolved,  therefore,  burns 
principally  here,  whilst  the  carbon  separates  in  a  state  of 
intense  white  heat,  and  is  thus  the  cause  of  the  luminous- 
ness  of  this  part.  In  the  outer  coat,  the  access  of  air  is 
no  longer  limited,  and  all  the  gases  not  yet  consumed,  are 
consumed  there.  This  part  of  the  flame  is  the  hottest. 
Oxidizable  bodies,  therefore,  oxidize  with  the  greatest  pos- 
sible rapidity  when  placed  in  it,  as  the  conditions  of  oxi- 
dizement  are  here  combined,  viz.  high  temperature, 
and  an  unlimited  supply  of  oxygen.  This  part  of  the 
flame  is  therefore  called  the  oxydizing  flame.  But  the 
contrary  ensues  when  we  place  oxydized  bodies  having  a 
tendency  to  yield  up  their  oxygen,  within  the  luminous 
part  of  the  flame,  i.  e.  these  substances  lose  their  oxygen, 
the  carbon  and  the  still  unconsumed  carburetted  hydro- 
gen withdraw  it  from  them,  and  thus  reduce  them.  The 
luminous  part  of  the  flame  is  therefore  called  the  reducing 
flame.  Now,  if  we  conduct  a  fine  stream  of  air  into  a 
flame,  we  have  oxygen,  not  merely  around  the  outward 
flame,  but  also  in  its  interior  part.  Combustion  takes 
place,  therefore,  in  either  part.  But  this  air  rushes  with  a 
certain  vehemence  into  the  flame,  and  carries  forward  the 
gases  evolved,  mixes  intimately  with  them,  and  effects 
their  combustion  at  a  certain  distance  from  the  point  of  the 
blow-pipe.  This  spot  is  marked  by  a  bluish  light.  It  is 


28  USE    OF    THE    BLOW-PIPE. 

the  hottest  of  the  whole  flame,  since  the  combustion  is 
most  complete  there,  owing  to  the  intimate  intermixture 
of  the  air  with  the  gases.  The  luminous  part  of  the  flame 
being  thus  surrounded  on  all  sides  by  very  hot  flames,  its 
temperature  also  becomes  exceedingly  elevated,  and  this 
elevation  of  temperature  is  the  principal  object  in  the  ap- 
plication of  the  blow-pipe  ;  the  hottest  point  is  then,  of 
course,  somewhat  before  the  aperture  of  the  blow-pipe.  In 
this  reducing  flame  many  bodies  fuse  with  ease,  which  re- 
main unaltered  in  a  common  flame.  The  heat  of  the  oxi- 
dizing flame  also  is  considerably  increased  by  the  blow- 
pipe, since  it  becomes  more  concentrated  upon  one  point. 

As  fuel  we  use  either  an  oil-lamp,  or  a  wax  candle,  or 
a  lamp  fed  with  a  solution  of  oil  of  turpentine  in  spirits  of 
wine.  A  common  spirit-lamp  does  not  yield,  in  all  cases, 
the  requisite  degree  of  heat. 

The  blowing  is  effected  by  the  cheek-muscles  alone, 
and  not  by  the  lungs.  This  way  of  blowing  may  easily 
be  acquired  by  practising  for  some  time  to  breathe  gently, 
with  puffed  up  cheeks.  If  by  this  means  the  student  has 
succeeded  so  far  as  to  be  able  to  continue  calmly  breath- 
ing in  this  manner,  even  when  holding  the  blow-pipe  be- 
tween his  lips,  nothing  except  a  little  practice  will  be  re- 
quired to  enable  him  to  produce  a  continuous,  correct  and 
steady  flame. 

The  supports  on  which  the  substances  to  be  examined 
are  exposed  to  the  flame  of  the  blow-pipe,  are  usually 
either  charcoal,  platinum  wire,  or  platinum  plate.  In  the 
choice  of  charcoal  for  the  purpose  of  blow-pipe  experi- 
ments, we  must  especially  look  to  its  being  thoroughly 
charred,  because,  if  not  so,  it  will  split  and  throw  off  the 
substances  placed  on  it.  The  substances  to  be  examined 
are  put  into  small  conical  cavities  carved  into  the  piece  of 
charcoal  by  means  of  a  pen-knife.  We  generally  employ 
charcoal  as  a  support,  when  we  want  to  reduce  a  metallic 
oxide,  or  to  test  its  substance  as  to  its  fusibility.  If  metals 
are  volatile  in  the  heat  of  the  reducing  flame,  they  evapo- 
rate partly  or  entirely  during  their  reduction.  But  these 
metallic  vapours  reoxidize  in  their  transit  through  the  ex- 
ternal flame. 

Many  of  them  have  a  peculiar  colour,  by  means  of 
which  the  metals  maybe  detected.  The  platinum  wire, 


APPARATUS  AND   UTENSILS.  29 

as  weU  as  the  platinum  plate,  should  be  selected  rather 
thin.  vVe  generally  make  use  of  platinum  wire  when  fus- 
ing bodies  together,  by  means  of  fluxes,  in  order  to  ascer- 
tain their  nature,  by  the  colour  and  other  properties  of  the 
button  produced. 

The  blow-pipe  flame  is  of  especial  importance  in  chem- 
ical experiments,  because  its  effects  yield  immediate  re^ 
suits.  These  are  of  two  different  kinds  ;  either,  1st,  we  ob- 
tain merely  a  knowledge  of  the  general  properties  of  the 
body,  and  are  consequently  only  enabled  to  determine  the 
class  to  which  it  belongs,  i.  e.  we  ascertain  whether  it  is  a 
fixed,  volatile,  or  fusible  substance,  &c.  &c.  ;  or,  2d,  the 
phenomena  we  observe  at  once  point  out  what  special  body 
we  have  before  us.  The  phenomena  in  question,  we  shall 
have  occasion  to  examine  when  we  treat  of  the  relation  of 
various  substances  to  reagents. 


APPENDIX  TO  THE  FIRST  CHAPTER, 
§  13. 

APPARATUS    AND    UTENSILS. 

As  the  student  cannot  be  supposed  to  know  the  appa- 
ratus, &c.,  necessary  for  chemical  analysis,  it  may  be  well 
here  to  furnish  him  with  a  list  of  indispensable  articles, 
and  to  point  out  the  qualities  they  should  possess,  in  order 
to  guide  him  in  their  purchase. 

1.  A  BERZELIUS  SPIRIT-LAMP.     The  vessel  containing 
the  spirit  of  wine  should  be  connected  with  the  wick  by 
means  of  a  narrow  tube,  to  avoid  explosions  j — the  chimney 
should  not  be  too  narrow.     The  aperture  through  which 
the  spirit  of  wine  is  poured  should  not  be  air-light. 

2.  A  LAMP-STAND  with  moveable  rings  and  brackets. 

3.  A  GLASS  SPIRIT-LAMP  with  ground  cover  and  brass 
wick-tube. 


30  APPARATUS    AND    UTENSILS. 

4.  A  BRASS  BLOW-PIPE  with  a  mouth-piece  made  «f  horn 
or  bone,  (vide  §  12.)     The  longer  tube    may  be  about 
seven  inches,  slightly  varying,  of  course,  according  to  the 
visual  distance  of  the  individual ;  the  length  of  the  smaller 
tube  ought  to  be  about  two  inches.     Both  must  be  ground 
air-tight  into  the  small  vessel,  which,  as  we  have  stated, 
(§  12,)  collects  and  retains  the  moisture  of  the  air  blown 
through  the  pipe.     It  is  advisable  to  keep  two  small  tubes 
at  hand,  one  with  a  wider,  and  the  other  with  a  narrower 
opening. 

5.  A.   PLATINUM   CRUCIBLE   with  ground   cover ;    this 
should  not  be  too  deep,  in  proportion  to  its  breadth. 

6.  A  PLATINUM  SPATULA  ;  this  ought  not  to  be  selected 
too  thin,  and  must  be  as  clean  and.  even  as  possible,  and 
about  two  inches  long  and  one  inch  in  breadth. 

7.  A  FEW  PIECES  OF  PLATINUM  WIRE,  of  the  S1Z6  of  hlte- 

strings,  varying  in  length  from  three  to  four  inches,  and 
twisted  at  both  ends  into  a  small  loop.  It  is  advisable  to 
keep  these  wires  in  a  small  glass  containing  water. 

8.  A  STAND  WITH  FROM  TWELVE  TO  TWENTY  TEST  TUBES. 

The  latter  may  vary  from  four  to  six  or  eight  inches  in 
length,  and  must  be  of  different  width.  They  should  be 
made  of  thin  white  glass,  and  so  well  annealed,  that  they 
do  not  crack  even  if  boiling  water  be  poured  into  them. 
Their  brim  must  be  quite  round,  and  slightly  turned  down ; 
it  ought  to  have  no  lip  whatever,  as  the  latter  is  not  of  the 
slightest  use,  and  prevents  the  tube  from  being  closely 
stopped  with*  the  ringer. 

9.  SEVERAL  BEAKER  GLASSES  AND  SMALL  RETORTS  of 
thin,  well-annealed  glass. 

10.  SEVERAL  PORCELAIN   EVAPORATING  DISHES,  AND  A 

VARIETY  OF  SMALL  PORCELAIN  CRUCIBLES.       ThoSC    of  the 

royal  manufacture  of  Berlin  are  quite  unexceptionable  in 
shape  as  well  as  durability. 

11.  SEVERAL  GLASS  FUNNELS  of  various  sizes.     They 
must  be  inclined  at  an  angle  of  sixty  degrees,  and  ought  to 
merge  into  their  tube  at  a  definite  angle. 

12-  A  SYRINGE  BOTTLE,  capable  of  holding  from  twelve 
to  sixteen  ounces  of  water,  (vide  §  5.) 

13.  SEVERAL  GLASS  RODS  AND  VARIOUS   GLASS   TUBES. 


REAGENTS.  31 

The  latter  may  be  bent,  drawn  out,  &c.,  over  a  Berzelius 
spirit-lamp. 

14.  A  selection  of  WATCH-GLASSES. 

15.  A  small  AGATE  MORTAR. 

16.  Several  small  IRON  SPOONS. 

17.  A  pair  of  small  PINCERS,  with  scissor-handles,  the 
blades  close  together,  and  bent  at  their  extremity  at  an 
obtuse  angle. 

These  should  be  varnished. 


CHAPTER    II 

REAGENTS. 


VARIOUS  phenomena  may  manifest  themselves  during 
the  decomposition  or  combination  of  bodies.  In  some 
cases  liquids  change  their  colour,  in  others  precipitates 
are  formed,  sometimes  effervescence  takes  place,  and 
sometimes  deflagration,  &c.  Now,  if  these  phenomena 
are  very  striking,  and  if  they  accompany  only  the  com- 
bination or  decomposition  of  two  definite  bodies,  it  be- 
comes evident  that  by  means  of  one  of  these  bodies  the 
presence  of  the  other  may  be  detected  and  proved  :  e.  g. 
if  we  know  that  a  white  precipitate,  of  determinate  pro- 
perties, is  formed  on  mixing  barytes  with  sulphuric  acid, 
there  can  be  no  difficulty  in  understanding  that,  if  by 
adding  barytes  to  any  liquid  we  obtain  a  precipitate  of 
these  determinate  properties,  the  conclusion  must  follow, 
that  this  liquid  contains  sulphuric  acid.  « 

Those  substances  which  indicate  the  presence  of  other 
bodies,  by  somewhat  striking  phenomena,  are  called 
reagents^  on  account  of  their  mutual  action  upon  each 
other. 

Reagents  are  divided  into  general  and  special,  accord- 
ing to  the  object  obtained  by  their  application.  By  general 
reagents,  we  understand  those  by  means  of  which  we  deter- 


32  REAGENTS. 

mine  the  class  or  group  to  which  the  substance  under  in- 
vestigation belongs  ;  and  by  special  reagents  those,  by 
means  of  which  we  detect  a  single  definite  substance.  It 
c'annot  be  considered  an  objection  to  this  classification, 
that  the  limits  between  these  two  divisions  cannot  be 
drawn  with  any  degree  of  exactness.  I  suggest  it  only 
to  induce  the  student  to  keep  distinctly  in  view  his  pre- 
cise object,  i.  e.  whether  a  group  is  to  be  determined  or  a 
single  substance. 

The  value  of  reagents  depends  on  two  circumstances  : 
1st,  whether  they  are  characteristic ;  and  2d,  whether 
they  are  sensible.  We  call  a  reagent  characteristic,  if 
the  alteration  it  produces  by  the  detection  of  the  sub- 
stance, the  presence  of  which  (in  -mixture  or  combination) 
we  wish  to  ascertain,  is  of  so  distinct  a  character  as  to 
admit  of  no  erroneous  conclusion.  Thus,  iron  is  a  charac- 
t&ristic  reagent  for  copper,  protochloride  of  tin  for, mer- 
cury, because  the  phenomena  thereby  produced,  such*  as 
the  separation  of  metallic  copper  and  of  globular  mercury, 
admit  of  no  mistake.  We  call  a  reagent  sensible,  if  its 
action  is  still  clearly  perceptible,  although  but  a  very  small 
qtfantity  of  the  substance  to  be  detected  may  be  present, 
&*  g.  the  action  of  starch  upon  iodine.  We  need  scarcely 
mention  that  reagents  "must  in  general  be  chemically  pure ; 
they  must  contain  no  foreign  substance,  but  simply  consist 
of  their  essential  constituents,  for  their  evidence  cannot 
be  relied  upon  if  this  be  not  the  case.  We  must  there- 
fore make  it  a  rule  carefully  to  test  reagents  as  to  their 
purity,  before  we  use  them  in  experiments,  no  matter  whe- 
ther they  be  articles  of  our  own  production  or  of  purchase. 
As  a  matter  of  course,  in  the  instruction  we  shall  give 
when  treating  of  each  reagent  in  particular,  and  of  the 
mode  of  testing  its  purity,  we  cannot  take  cognizance  of 
all  those  substances  with  which  the  reagent  may,  acci- 
dentally, have  become  mixed,  but  only  of  those,  the  pre- 
sence of  which  is  probable  from  the  manner  of  its  prepa- 
ration. 

One  of  the  most  common  sources  of  mistakes  in  quali- 
tative analysis,  proceeds  from  missing  the  proper  measure 
— the  right  quantity — in  the  addition  of  a  reagent  to  a  sub- 
stance under  examination.  Such  terms  as  "  addition  in 


&EAGENTS,  83 

excess,"  l<  supersaturation,"  &c.,  often  induce  novices  er- 
roneously to  suppose  that  they  cannot  add  too  much  of  the 
reagent^  and,  to  avoid  using  too  small  quantities,  many  fill 
a  test  cylinder  with  acid  for  the  supersaturation  of  a  few 
drops  of  an  alkaline  fluid,  whilst  yet  every  drop  of  acid 
added,  after  the  neutralization  point  has  once  been  reached, 
must  be  considered  an  excess  of  acid.  But,  on  the  other 
hand,  an  insufficient  addition  is  just  as  much  to  be  avoided 
as  a  too  copious  one,  since  a  reagent  in  insufficient  quan- 
tity often  produces  phenomena  quite  different  from  those 
manifested  when  added  in  excess  :  e.  g.  chloride  of  mer- 
cury, wheji  treated  with  a  small  quantity  of  sulphuretted 
hydrogen,  gives  a  white  precipitate  ;  but  when  treated  with 
sulphuretted  hydrogen  in  excess,  the  precipitate  is  black. 
Experience  has,  however,  proved  that  the  most  common 
mistake  beginners  are  liable  to,  and  which  renders  their 
operations  difficult  and  uncertain,  is  to  add  the  reagents  in 
too  copious  quantities.  The  reason  why  the  experiment 
loses  thereby  in  certainty,  is  clear,  if  we  recollect  that  all 
the  changes  effected  by  reagents  are  perceptible  only 
within  certain  limits,  and  that  consequently  they  become 
less  and  less  evident,  and  may  the  easier  be  overlooked 
the  more  we  approach  this  point  by  diluting  the  fluid. 

No  definite  rules  can  be  given  for  avoiding  this  source 
of  errors  ;  a  general  rule  may,  however,  be  laid  down, 
and  this  even  is  sufficient  to  point  out  the  proper  measure 
in  all,  or  at  least  in  most  cases.  It  is  simply  this  :  let  the 
student  always,  before  the  application  of  a  reagent,  well 
consider  to  what  purpose  he  applies  it,  and  what  are  the 
phenomena  he  intends  to  produce. 

We  divide  reagents  into  two  classes,  according  as  the 
fluid  state  of  substances,  indispensable  to  the  action  of 
the  reagents,  is  caused  either  by  the  application  of  heat, 
or  by  means  of  liquid  solvents;  viz.  1,  Reagents  in  the 
humid  way  ;  and  2,  Reagents  in  the  dry  way.  For  the 
sake  of  facility  and  simplicity,  we  subdivide  these  two 
classes  as  follows  : — 

A.  REAGENTS  IN  THE  HUMID  WAY. 

I.  GENERAL  REAGENTS. 

a.  Reagents  principally  used  as  SIMPLE  SOLVENTS. 


34  WATER. 

b.  Reagents  principally  used  as  CHEMICAL  SOLVENTS. 

c.  Reagents  which  serve    especially   to   separate,    or 
otherwise  to  characterise  groups  of  substances. 

II.  SPECIAL  REAGENTS. 

a.  Reagents  which  serve  especially  for  the  detection  of 
the  various  BASES. 

6*  Reagents  which  are  particularly  applied  to  the  de- 
tection of  the  various  ACIDS. 

B.  REAGENTS  IN  THE  DRY  WAY. 

I.  FLUXES. 

II.  BLOW-PIPE    REAGENTS. 

A.  REAGENTS  IN  THE  HUMID  WAY. 

I.  GENERAL  REAGENTS. 
a.  Reagents  principally  used  as  simple  solvents. 

§   15. 
1.  WATER.     (H  O.) 

Preparation. — Pure  water  is  obtained  by  distilling 
spring-water  from  a  copper  still,  or  from  a  glass  retort. 
This  distillation  should  not  be  carried  beyond  three-fourths 
of  its  quantity.  Rain-water  received  in  the  open  air  may 
in  most  cases  be  substituted  for  distilled  water. 

Testing. — Distilled  water  must  leave  no  residue  on 
evaporation,  and  must  not  alter  the  colour  of  Georgina 
paper.  Nitrate  of  silver,  chloride  of  barium,  oxalate  of 
ammonia,  and  lime-water,  should  not  disturb  its  transpa- 
rency. 

Uses.— We  use  water*  chiefly  as  a  simple  solvent  for 
a  great  variety  of  substances.  It  has,  moreover,  a  special 
application  for  the  decomposition  of  several  neutral  metaj- 
lic  salts,  giving  rise  to  the  formation  of  soluble  acid,  and 
insoluble  basic  compounds  ;  this  is  particularly  the  case 
with  the  salts  of  bismuth  and  the  chloride  of  antimony. 

*  In  chemical  experiments  we  never  make  use  of  any  other  but 
distilled  water ;  whenever  therefore  the  term  "  water"  occurs  in  the 
present  work,  distilled  water  is  meant. 


ALCOHOL.      ETHER.      HYDROCHLORIC    ACID.  35 


2.    ALCOHOL.       (C4  H6   O2  =  E,    O  +  Aq.) 

Preparation.  —  Two  sorts  of  alcohol  are  used  in  chemi- 
cal analysis  ;  1st.  spirit  of  wine  of  0'83  or  0*84,  (spiritus 
vini  rectificatissimus  of  the  shops  ;)  and  2d,.  absolute 
alcohol.  The  latter  may.be  obtained  by  distilling  the 
former,  with  the  addition  of  fused  chloride  of  calcium. 

Testing.  —  Pure  alcohol  must  completely  volatilize, 
and  ought  not  to  cause  any  enipyreumatic  smell  when 
rubbed  between  the  hands,  nor  should  it  redden  litmus 
paper. 

Uses.  —  Many  substances  are  soluble  in  alcohol,  others 
remain  insoluble.  It  may,  therefore,  frequently  be  em- 
ployed for  the  separation  of  the  former  from  the  latter,  e. 
g.  of  chloride  of  strontium  from  chloride  of  barium.  We 
use  alcohol  also  to  precipitate  from  their  aqueous  solutions 
such  substances  as  are  insoluble  in  alcohol,  e.  g.  to  pre- 
cipitate malate  of  lime.  We  employ  alcohol,  moreover, 
in  the  production  of  various  kinds  of  ether,  especially  of 
ascetic  ether,  (which  is  so  particularly  characterised  by 
its  agreeable  odour.)  Alcohol  serves  also  for  the  detection 
of  various  substances  which  impart  a  characteristic  tint  to 
its  flame,  especially  boracic  acid,  strontian,  soda,  and  potash. 

§17. 

3.    ETHER.       (C4  H5  O  =  E  O.) 

Ether  has  but  a  very  limited  application  in  the  analysis 
of  inorganic  bodies.  We  use  it  in  fact  only  to  detect  and 
isolate  bromine,  (§  100,  6.)  and  for  this  purpose  commer- 
cial officinal  ether  is  sufficiently  pure  and  strong. 

b.  Reagents  which  are  principally  used  as  chemical 
solvents. 


7 


§  18. 

1.    HYDROCHLORIC   ACID.  '    (Cl  H.) 

Preparation. — A  mixture  of  thirteen  and  a  half  parts 
of  oil  of  vitriol  and  four  parts  of  water,  when  cold,  is 


ACID. 

poured  upon  eight  parts  of  common  salt  contained  in  a 
retort  ]  the  neck  of  the  retort  is  then  somewhat  raised,  and 
the  heat  of  the  sand-bath  applied  to  the  latter,  as  long  as 
gas  passes  over.  The  gas  evolved  is  by  means  of  a  bent 
tube,  transmitted  through  twelve  parts  of  water,  in  a  glass 
flask,  which  must  be  constantly  kept  cool.  In  order  to 
prevent  the  gas  from  receding,  the  tube  is  only  permitted 
to  dip  about  one  line  into  the  water  of  the  receiver.  If 
the  sulphuric  acid  contains  nitric  acid,  the  gas  which 
passes  over  first,  (and  which  in  that  case  contains  chlorine,) 
must  be  received  separately.  The  hydrochloric  acid  thus 
produced  is  tested  as  to  its  specific  gravity,  and  diluted 
with  water  until  its  specific  gravity  is  I'll  or  1*12. 

Testing. — Hydrochloric  acid,  used  for  the  purposes  of 
chemical  analysis,  must  be  colourless  and  leave  no  residue 
upon  evaporation,  nor  ought  it  to  discolour  indigo-solution, 
even  when  heated  with  it  to  boiling.  Chloride  of  barium 
ought  not  to  produce  any  precipitate  of  barytes,  neither  in 
the  highly  diluted  acid,  (sulphuric  acid,)  nor  even  after 
having  been  boiled  with  nitric  acid,  (sulphurous  acid.) 
Sulphuretted  hydrogen  must  leave  it  unaltered.  Ferro- 
cyanide  of  potassium  must  not  cause  any  precipitate  in  it, 
nor  even  impart  the  slightest  blue  tinge  to  it,  after  neu- 
tralization with  ammonia  and  subsequent  addition  of  some 
acetic  acid  in  excess. 

Uses. — We  employ  hydrochloric  acid  as  a  chemical  sol- 
vent for  a  very  great  variety  of  bodies,  especially  for  oxides 
and  peroxides  (on  the  solution  of  which,  chlorine  is  libera- 
ted,) and  salts  with  weaker  acids.  A  solution  of  this  kind, 
always  depends  on  the  formation  of  a  chloride  soluble  in 
water.  Muriatic  acid  serves  also  as  a  simple  solvent  for 
many  salts,  e.  g.  the  phosphates,  borates,  and  oxalates  of 
the  alkaline  earths.  We  use  it,  moreover,  to  expel  weaker 
acids  from  their  salts  ;  e.  g.  carbonic  acid,  hydro'sulphuric 
acid.  It  has  also  a  special  application  in  the  detection 
and  precipitation  of  oxyde  of  silver,  protoxyde  of  mercury, 
and  oxyde  of  lead,  (vide  infra,)  as  well  as  in  the  detection 
of  free  ammonia,  by  producing  dense  white  fumes  with  it, 
dependent  on  the  formation  of  sal  ammoniac,  in  the  air. 


NITRO-MURIATIC  ACID.    AQUA  REGIA.  37 


.    f 


2.       NITRIC    ACID,       (NO5.) 

Preparation.  —  The  nitric  acid  of  commerce  almost  in- 
variably contains  sulphuric  acid  and  hydrochloric  acid.  In 
order  to  purify  it  for  the  purpose  of  chemical  analysis,  a 
solution  of  nitrate  of  silver  is  added  to  it,  as  long  as  any 
precipitate  of  chloride  of  silver  is  formed  ;  this  precipitate 
is  allowed  to  settle,  and  the  supernatant  acid  decanted  into 
a  retort,  and  distilled  to  within  a  small  fraction  of  its  whole 
amount.  The  distillate  is  then,  if  necessary,  diluted  with 
water  till  the  acid  has  a  specific  gravity  of  1'2. 

Testing.  —  Pure  nitric  acid  must  be  colourless,  and, 
when  evaporated  on  a  platinum  plate,  leave  no  residue 
behind.  Nitrate  of  barytes,  or  nitrate  of  silver,  must  not 
render  it  turbid.  It  is  advisable  to  dilute  the  acid  highly 
with  water  before  the  application  of  these  reagents,  since 
nitrates  will  be  precipitated  if  this  precaution  be  neglected. 

Uses,  —  Nitric  acid  serves,  in  the  first  place,  as  a  chemi- 
cal solvent  for  metals,  oxides,  sulphurets,  oxygen  salts, 
&c.  Its  action  on  metals  and  sulphurets  depends  on  the 
oxidation  of  these  bodies,  at  the  expense  of  part  of  its 
oxygen,  and  on  the  subsequent  chemical  solution  of  the 
thereby  formed  oxides,  giving  rise  to  the  formation  of  ni- 
trates. Most  oxides  dissolve  in  nitric  acid,  directly  as 
nitrates,  and  the  same  is  the  case  with  most  insoluble  — 
(i.  e.  in  water)  —  salts  with  weaker  acids,  the  nitric  acids 
expelling  the  latter.  For  many  salts  with  stronger  acids 
it  is  (like  hydrochloric  acid)  used  as  a  simple  solvent,  e.  g. 
the  phosphates  of  the  alkaline  earths.  Nitric  acid  serves, 
moreover,  as  the  most  common  means  of  oxidation  ;  thus 
we  use  it,  for  instance,  to  convert  protoxide  of  iron  into 
peroxide,  to  decompose  hydriodic  acid  and  the  iodides,  &c. 

§  20. 

NITRO-MURIATIC    ACID.       AQUA   REGIA.       (NO4+C1.) 

Preparation.  —  One  measure  of  pure  nitric  acid  is  mixed 
with  from  three  to  four  measures  of  pure  hydrochloric  acid. 
Uses.  —  Nitric  acid  and  hydrochloric  acid  decompose 
2 


00  ACETIC    ACID. 

each  other  in  such  a  manner  as  to  give  rise  to  the  forma- 
tion of  chlorine,  hyponitric  acid,  and  water*  This  decom- 
position ceases  as  soon  as  the  liquid  is  saturated  with 
chlorine,  but  it  is  resumed  immediately,  if  this  state  of 
saturation  is  disturbed,  by  the  application  of  heat,  or  by 
the  chlorine  combining  with  some  other  substance.  Thus 
we  have,  in  aqua  regia,  1st,  a  continuous  source  of  chlo- 
rine ;  and  2d,  hyponitric  acid,  and  consequently  a  com- 
bination which  has  the  property  of  readily  yielding  oxygen. 
The  mixture  of  those  two  substances  renders  aqua  regia 
the  most  powerful  solvent  we  possess  for  metals,  (those 
excepted  which  form  insoluble  compounds,  with  chlorine.) 
We  use  aqua  regia  chiefly  for  the  solution  of  gold  and 
platinum,  (both  of  which  are  insoluble  in  hydrochloric  "acid 
alone,  as  well  as  in  nitric  acid  alone,)  and  for  the  decom- 
position of  various  sulphurets,  e.  g.  cinnabar,  &e. 

§  21. 

4,     ACETIC    ACID.       (C4H3O3=A.) 

Preparation.— Pure  acetic  acid  is  best  obtained  by 
rubbing  ten  parts  of  crystallized  neutral  acetate  of  lead 
together,  with  three  parts  of  anhydrous  sulphate  of  soda, 
pouring  the  mixture  into  a  retort,  adding  a  cooled  mixture 
of  two  and  a  half  parts  of  sulphuric  acid,  with  an  equal 
weight  of  water,  and  distilling  to  dryness,  in  a  sand-bath. 
The  receiver  is  best  connected  with  the  retort  by  means  of 
a  Liebig's  condensing  apparatus. 

Testing. — Pure  acetic  acid  must  leave  no  residue  upon 
evaporation.  Sulphuretted  hydrogen,  and  solution  of  sil- 
ver and  of  barytes,  must  not  precipitate  it  when  diluted, 
solution  of  barytes  not  even  when  the  acetic  acid  has  been 
previously  boiled  with  nitric  acid.  Indigo  solution  must 
not  be  discoloured  on  being  heated  with  the  acid,  (vide 
§  101,  a.) 

Uses. — The  application  of  acetic  acid  in  qualitative 
analysis  is  chiefly  based  upon  its  possessing  an  unequal 
power  of  solution  for  different  substances,  so  it  serves,  for 
instance,  to  distinguish  oxalate  of  lime  from  phosphate  of 
lime.  We  apply  acetic  acid  also  for  the  acidulation  of 
liquids,  -when  we  wish  to  avoid  the  use  of  mineral  acids. 


CHLORIDE    OF   AMMONIUM.  39 

,        §  22.  *l 

5.     CHLORIDE    OF    AMMONIUM.       (N  H4    Cl.) 

Muriate  of  Ammonia. 

Preparation.— The  sal  ammoniac  of  commerce  may 
generally  be  purified  for  the  purposes  of  chemical  analysis 
by  simple  recrystallization.  If  it  contains  iron,  a  small 
quantity  of  hydros ulphuret  of  ammonia  must  be  added  to 
the  solution ;  the  precipitate  formed  is  allowed  to  settle, 
the  solution  filtered,  and  hydrochloric  acid  added  to  it  until 
a  feeble  acid  re-action  manifests  itself ;  the  mixture  then 
is  boiled,  filtered,  saturated  with  ammonia,  and  crystal- 
lized. For  use  as  a  reagent,  one  part  of  the  salt  is  dis- 
solved in  eight  parts  of  water. 

Testing. — Solution  of  sal  ammoniac,  when  evaporated 
on  a  platinum  plate,  must  leave  a  residue  which  com- 
pletely volatilizes  upon  a  higher  degree  of  heat  being  ap- 
plied. Hydrosulphuret  of  ammonia  ought  not  to  change 
it.  Its  reaction  ought  to  be  completely  neutral. 

Uses. — We  employ  sal  ammoniac  chiefly  to  keep  in  so- 
lution certain  oxides,  e-  g.  protoxide  of  manganese,  mag- 
nesia, or  certain  salts,  e.  g.  tartrate  of  lime,  when  other 
oxides  or  salts  are  precipitated  by  ammonia  or  by  some 
other  reagents.  This  application  of  sal  ammoniac  is  based 
on  the  tendency  of  the  ammoniacal  salts  to  form  double 
combinations  with  other  salts.  Sal  ammoniac  also  serves 
to  distinguish  between  precipitates  possessed  of  similar 
properties,  e.  g.  to  distinguish  the  basic  phosphate  of  mag- 
nesia and  ammonia  which  is  insoluble  in  sal  ammoniac, 
from  other  precipitates  of  magnesia.  We  employ  sal  am- 
moniac besides  to  precipitate  from  their  solutions,  various 
substances  soluble  in  potash,  and  insoluble  in  ammonia, 
e.  g.  alumina,  oxide  of  chromium ;  for  in  this  process  the 
sal  ammonia  decomposes  with  the  potash,  and  chloride  of 
potassium,  water,  and  ammonia  are  formed.  Sal  ammo- 
niac is  moreover  specially  used  to  precipitate  platinum  as 
ammonio  chloride  of  platinum. 


40  REAGENT    PAPERS.       GEORGINA    PAPERS. 


c.  Reagents  which  serve  especially  to  separate  or  other- 
wise to  characterize  groups  of  substances. 

§  23. 

1.    REAGENT  PAPERS  :    <*>.    BLUE    LITMUS    PAPER. 

Preparation. — One  part  of  commercial  litmus  is  digested 
with  six  parts  of  water  ;  the  intensely  blue  liquid  obtained 
is  divided  into  two  parts,  and  the  free  alkali  contained  in 
the  one  half  saturated  by  stirring  it  repeatedly  with  a  glass 
rod  dipped  into  very  dilute  sulphuric  acid,  until  the  colour 
exhibits  a  shade  of  red ;  then  the  other  blue  half  is  added, 
the  whole  poured  into  a  cup,  and  slips  of  fine  unsized  pa- 
per are  dipped  into  this  tincture.  These  slips  are  then 
suspended  on  threads  for  the  purpose  of  drying.  The 
colour  of  litmus  paper  must  be  uniform,  and  neither  too 
light  nor  too  dark. 

Uses. — Litmus  paper  serves  for  the  detection  of  free 
acids  in  liquids,  since  its  blue  colour  becomes  thereby 
changed  into  red.  It  must,  however,  be  borne  in  mind, 
that  it  undergoes  the  same  alteration  by  the  neutral  salts 
of  most  metallic  oxides. 

ft.  REDDENED  LITMUS  PAPER. 

Preparation. — Blue  litmus  tincture  is  repeatedly  stirred 
wilh  a  glass  rod  dipped  into  dilute  sulphuric  acid,  until  its 
colour  has  assumed  a  distinct  shade  of  red.  Slips  of  pa- 
per are  then  dipped  into  this  tincture.  They  must  be 
distinctly  red  when  dry.4 

Uses. — The  blue  colour  of  reddened  litmus  paper  is 
restored  by  pure  alkalies  and  alkaline  earths,  as  well  as 
by  their  sulphur  combinations,  by  alkaline  carbonates,  and 
also  by  the  soluble  salts  of  several  other  weak  acids, 
especially  of  boracic  acid.  It  serves,  therefore,  for  the  de- 
tection of  these  substances  in  general. 

V.   GEORGINA   PAPER. 

Preparation- — The  violet  coloured  petals  of  Georgina 
purpurea  are  boiled  in  water  or  digested  with  spirits  of 


TURMERIC    PAPER.      SULPHURIC   ACID.  41 

wine,  and  slips  of  paper  dipped  into  the  tincture.  Care 
should  be  taken  to  concentrate  the  liquor  only  to  such  a 
degree  as  to  impart  to  the  paper  when  dry,  a  fine  violet- 
blue  colour,  which  must  not  be  too  dark  (deep.)  A  small 
quantity  of  ammonia  is  added  to  the  tincture,  if  the  colour 
is  too  red. 

Uses.  —  Georgina  paper  is  reddened  by  acids  ;  alkalies 
impart  a  beautiful  green  tinge  to  it.  It  is,  therefore,  of  very 
convenient  application,  as  a  substitute  for  the  blue  as  well 
as  the  red  litmus  paper.  It  is  of  extreme  susceptibility,  if 
properly  prepared,  for  acids  as  well  as  for  alkalies.  Con- 
centrated solutions  of  caustic  alkalies,  colour  it  yellow  by 
destroying  its  colouring  matter. 


.    TURMERIC   PAPER. 

* 

Preparation.  —  One  part  of  bruised  turmeric-root  is  di- 
gested and  heated  with  six  parts  of  dilute  spirit  of  wine  ; 
the  tincture  obtained  is  filtered,  and  slips  of  fine  paper  are 
dipped  into  it.  Turmeric  paper,  when  dry,  must  have  a 
fine  yellow  colour. 

Uses.  —  It  serves  in  the  same  manner  as  reddened  litmus 
paper  and  Georgina  paper,  for  the  detection  of  free  alka- 
lies, &c.  ;  as  they  change  its  yellow  colour  into  brown. 
It  is  not  so  susceptible  as  the  other  reagent  papers,  but  the 
change  of  colour  it  produces  is  highly  characteristic,  and 
can  be  especially  well  perceived  in  several  coloured  li- 
quids ;  we  consequently  cannot  well  dispense  with  tur- 
meric paper.  It  must  be  borne  in  mind,  when  using  it  as 
a  test,  that,  besides  the  substances  mentioned  above,  (vide 
reddened  litmus  paper,)  several  other  bodies,  e.  g.  boracic 
acid,  change  its  yellow  colour  into  brown. 

All  reagent  papers  should  be  cut  into  slips,  and  kept  in 
well-closed  glass  jars  or  small  boxes. 

§  24.          ty' 

2.    SULPHURIC    ACID.       (S    O3.) 

English  sulphuric  acid  may  always  be  used  in  qualita- 


42  SULPHURETTED   HYDROGEN. 

live  analysis,  provided  it  contains  no  arsenic,  and  has  pre- 
viously been  freed  from  nitric  acid,  by  boiling.* 

Testing. — Pure  sulphuric  acid,  when  boiled  with  a 
small  quantity  of  indigo  solution,  must  not  destroy  its  blue 
colour.  When  mixed  with  pure  zinc  and  water,  it  must 
yield  hydrogen,  which,  on  being  passed  through  a  tube 
heated  to  redness,  does  not  deposit  the  slightest  crust  of 
arsenic.  (Compare  §  93,  d.) 

Uses. — Sulphuric  acid  having  to  most  bases  a  greater 
affinity  than  almost  any  other  acid,  is  principally  employed 
for  the  liberation  and  expulsion  of  other  acids,  especially 
of  phosphoric,  boracic,  muriatic,  nitric,  and  acetic  acids. 
Sulphuric  acid  serves  also  for  the  liberation  of  iodine  from 
the  iodides.  It  oxidizes,  in  this  process,*the  metals  at 
the  expense  of  its  own  oxygen,  and  is  converted  into  sul- 
phurous acid.  Several  substances  which  cannot  exist  in 
an  anhydrous  state  (e.  g.  oxalic  acid)  are  decomposed 
when  brought  into  contact  with  concentrated  sulphuric 
acid ;  this  decomposition  is  caused  by  the  great  affinity 
which  sulphuric  acid  has  for  water.  The  nature  of  the 
decomposed  body  may  in  such  cases  be  determined  by 
the  liberated  products  of  its  decomposition.  Sulphuric 
acid  is,  moreover,  frequently  used  for  the  evolution  of  sev- 
eral gases,  especially  of  hydrogen  and  sulphuretted  hy- 
drogen. It  is,  besides,  especially  employed  for  the  detec- 
tion and  precipitation  of  barytes,  strontian,  and  lead.  The 
acid  used  for  this  purpose  is  diluted  with  four  parts  of 
water. 


§  25. 

3.  SULPHURETTED  HYDROGE^.   (HS.) 


DROGEN. 


Preparation. — Mix  intimately  thirty-two  parts  of  iron 
filings  with  twenty-one  parts  of  sublimed  sulphur,  divide 
into  small  portions,  and  gradually  project  them  into  a  cru- 
cible heated  to  redness,  and  before  adding  new  portions, 
wait  until  the  last  are  red-hot.  Aftkr  the  entire  mixture 
has  thus  been  fused,  the  crucible  is  well  covered,  and  al- 

*  The  sulphuric  acid  of  commerce  often  contains  lead,  which  ren- 
ders it  turbid  when  diluted  ;  this  may  be  removed  by  allowing  the 
lead  to  subside,  or  by  distillation. — ED. 


SULPHURETTED   HYDROGEN.  43 

lowed  to  remain  a  short  time  longer  exposed  to  the  fire. 
The  sulphuret  of  iron  thus  obtained  is  broken  into  lumps, 
when  cool,  covered  with  water,  in  an  evolution  bottle 
(a,)  and  concentrated  sulphuric  acid 'added  by  means  of 
(through)  a  funnel  tube  (b.)  The  gas  evolved  is  transmit- 
ted through  some  water  (c.)  for  the  purpose  of  purifying 
it. 


Sulphuretted  hydrogen  water  is  prepared  by  conduct- 
ing the  gas  obtained  in  the  preceding  process  into  water  of 
the  lowest  possible  temperature  (d,)  until  it  is  saturated, 
consequently  until  the  whole  volume  of  the  gas  added  in 
excess  begins  to  escape  completely  unabsorbed.  Sul- 
phuretted hydrogen  water  must  be  kept  in  well-closed  ves- 
sels, as  it  soon  undergoes  complete  decomposition,  if  this 
precaution  is  neglected.  It  keeps  very  long  if  it  is  im- 
mediately after  preparation  put  into  little  flasks,  and  these 
latter,  being  well  corked,  are  placed  in  an  inverted  position 
into  small  vessels  filled  with  water.  Sulphuretted  hydro- 
gen water  must  be  clear,  possess  the  odour  of  the  gas  to  a 
high  degree,  and  yield  a  strong  precipitate  of  sulphur," 
when  treated  with  chloride  of  iron.  It  must  not  assume  a 
blackish  tinge  upon  the  addition  of  ammonia. 

Uses. — Sulphuretted  hydrogen  has  a  strong  tendency  to 
decompose  with  metallic  oxides,  forming  water  and  sul- 
phurets.  As  these  latter  are  mostly  insoluble  in  water,  a 
decomposition  of  this  kind  is  usually  attended  with  pre- 
cipitation of  the  metallic  oxides  from  their  solutions.  The 


44  HYDROSULPHURET    OP   AMMONIA. 

conditions  under  which  these  precipitations  take  place, 
differ  in  such  a  manner,  that  by  altering  them  we  are  en- 
abled to  divide  all  precipitable  metals  into  groups,  (as  we 
shall  afterwards  explain,  vide  §  26,  uses.)  Sulphuretted 
hydrogen  is,  therefore,  an  invaluable  means  for  the  division 
of  metals  into  groups.  Some  of  these  sulphuret  precipi- 
tates have  so  distinct  a  colour,  that  we  are  enabled  there- 
by to  determine  the  particular  metals  they  contain.  Sul- 
phuretted hydrogen  serves  for  the  special  detection  of  the 
following  metals  :  tin,  antimony,  arsenic,  cadmium,  man- 
ganese, and  zinc.  For  more  ample  information  we  refer 
the  reader  to  the  third  chapter.  From  it's  property  of 
being  readily  decomposed,  sulphuretted  hydrogen  serves 
also  as  means  of  reduction  for  many  substances  ;  thus, 
for  instance,  salts  of  peroxide  of  iron  are  converted  by  it 
into  salts  of  protoxide  of  iron,  chromic  acid  is  changed  into 
chromic  oxide,  &c.  Sulphur  separates  in  these  reduc- 
tions, in  the  form  of  a  white  powder. 

§  26. 

2.    HYDROSULPHTJRET    OF    AMMONIA.    (NH4SHS.) 

Preparation. — This  liquid  is  formed  by  transmitting 
sulphuretted  hydrogen  through  liquor  of  ammonia,  to  com- 
plete saturation,  consequently  till  it  no  longer  causes  pre- 
cipitation in  a  solution  of  sulphate  of  magnesia.  The  so- 
lution obtained  must  be  kept  in  well-closed  bottles,  since 
contact  with  the  atmosphere  decomposes  it. 

Testing. — Hpdrosulphuret  of  ammonia  is  transparent  at 
first,  and  yields  no  sulphur  on  being  mixed  with  acids  ;  in 
contact  with  the  atmosphere  .  it  assumes  a  yellow  tint 
caused  by  the  formation  of  sulphuret  of  ammonium,  in  ex- 
cess. This  yellow  tinge,  however,  does  not  render  the 
reagent  useless.  But  it  now  yields  sulphur  when  mixed 
with  acids,  and  this  ought  to  be  overlooked  in  experiments. 
Hydrosulphuret  of  ammonia  must  be  transparent,  and 
when  heated  evaporate  without  residue  :  and,  as  already 
mentioned  above,  ought  not  to  precipitate  solution  of  mag- 
nesia. 

Uses*  —  The  arrangement  into  groups  of  the  metallic  ox- 
ides, precipitable  by  sulphuretted  hydrogen,  depends  upon 


SULPHURET  OF  POTASSIUM.  POTASH.       45 

certain  conditions  indispensable  to  their  precipitation.  The 
presence  of  an  alkali  is  one  of  these  conditions — its  ab- 
sence is  another ;  i.  e.  certain  sulphurets  precipitate  only 
if  the  liquid  is  alkaline,  because  they  are  soluble  in  acids  ; 
others  precipitate  only  if  the  liquid  is  acid,  as  they  are 
soluble  in  alkaline  sulphurets.  Now,  hydrosulphuret  of 
ammonia  may  be  considered  as  a  reagent  in  which  sul- 
phuretted hydrogen  acts  in  conjunction  with  ammonia. 
Here,  we  have,  therefore,  as  well  as  those  conditions  which 
are  necessary  for  the  precipitation  of  the  first-mentioned 
group,  as  also  those  conditions  which  prevent  the  precipi- 
tation of  the  other  group  of  sulphurets,  or  cause  their  re- 
solution, when  those  precipitated  from  acid  solutions  are 
digested  with  the  reagent.  For  the  purposes  of  this  latter 
application,  the  hydrosulphuret  of  ammonia  must,  in  cer- 
tain cases,  contain  sulphur  in  excess.  Besides  the  sul- 
phurets the  precipitation  of  which  is  effected  by  the  joint 
action  of  sulphuretted  hydrogen  and  of  ammonia,  the  hy- 
drosulphuret of  ammonia  by  the  sole  action  of  its  ammo- 
nia, precipitates  oxide  of  chromium  and  alumina  as  hy- 
drated  oxides,  and  also  such  substances  as  are  only  dis- 
solved by  free  acids,  e.  g.  phosphate  of  lime,  dissolved  in 
hydrochloric  acid,  and  this  property  of  hydrosulphuret  of 
ammonia  must  not  be  lost  sight  of  in  experiments. 

§  27. 

SULPHURET    OF    POTASSIUM.       (KS5) 

Preparation. — This"reagent  must  not  be  kept  in  store, 
but  prepared  immediately  previous  to  its  application. 
It  maybe  produced  by  boiling  sulphur,  in  proper  propor- 
tions, with  solution  of  caustic  potash. 

Uses. — Sulphuret  of  potassium  must  be  substituted  for 
hydrosulphuret  of  ammonia,  when  sulphuret  of  copper  is 
to  be  separated  from  sulphur  combinations  soluble  in  al-4 
kaline  sulphurets,  e.  g.  from  sulphuret  of  tin,  because  the 
sulphuret  of  copper  is  not  quite  insoluble  in  hydrosulphuret 
of  ammonia. 

§  28.  i 

6.    POTASH.       (KOJ     I 

Preparation.—  One  ounce  of  pure  carbonate  of  potash 
2* 


46  POTASH. 

(§  29)  is  dissolved  in  twelve  ounces  of  water,  the  solution 
boiled  in  a  clean  iron  pan,  and  whilst  the  liquid  is  kept 
constantly  at  a  boiling  point,  hydrate  of  lime  added  in  small 
portions  until  a  portion  of  the  fluid  thus  obtained,  causes 
no  longer  any  effervesence  when  filtered  into  hydrochloric 
acid.  (The  proportions  used  are,  the  hydrate  of  about  one 
part  of  the  caustic  lime  in  two  parts  of  carbonate  of  pot- 
ash.) The  pan  is  then  taken  off  the  fire.  If  the  process 
has  been  conducted  exactly  according  to  the  direction  here 
given,  the  carbonate  of  lime  which  has  been  formed  will 
quickly  subside.  When  all  the  carbonate  of  lime  has  set- 
tled at  the  bottom  of  the  vessel,  the  supernatant  solution  of 
potash  may  be  filtered  through  bleached  linen,  and  the  fil- 
trate obtained  rapidly  evaporated  in  a  clean  iron  pan,  or 
more  properly  in  a  silver  basin,  until  four  ounces  only  re- 
main, which,  consequently,  will  give  a  specific  gravity  of 
T33.  Solution  of  potash  is  kept  best  in  small  bottles,  shut 
in  the  manner  of  glass  spirit-lamps  by  a  .ground-glass 
cover,  in  default  of  which  a  small  slip  of  paper  ought  to  be 
rolled  around  the  glass  stopper  of  a  common  bottle.  If 
this  precaution  be  neglected,  it  will  be  found  impossible, 
after  a  short  time,  to  take  the  stopper  off. 

Testing. — Pure  solution  of  potash  ought  to  be  colour- 
less. It  must  form  no  precipitate  with  chloride  of  barium 
nor  with  nitrate  of  silver,  when  supersaturated  with  nitric 
acid,  during  which  latter  operation  a  slight  effervesence 
only  ought  to  take  place.  It  must  leave  no  silicic  acid  be- 
hind, when  after  evaporation  to  dryness  the  residue  is 
washed  off  with  water.  It  ought  not  to  be  rendered  tur- 
bid on  being  heated  with  an  equal  measure  of  solution  of 
sal  ammoniac. 

Uses.  —  By  means  of  its  great  affinity  for  acids,  potash 
decomposes  the  salts  of  most  bases,  and  precipitates  there- 
fore from  their  solutions  all  those  salts  which  are  insoluble 
in  water.  Many  of  these  oxides  are  dissolved  by  potash 
in  excess,  e  g.  alumina,  oxide  of  chromium,  oxide  of  lead ; 
others  are  not,  e.  g.  oxide  of  iron,  oxide  of  bismuth,  &c. 
Potash  thus  furnishes  us  with  a  means  of  separating  the 
former  oxides  from  the  latter.  Potash,  besides,  dissolves 
many  salts,  (e.  g.  chromate  of  lead,)  sulphurets  a.  s. 
o.,  and  thus  enables  us  as  well  to  separate  as  to  dis- 


CARBONATE    OF    POTASH.  47 

tinguish  them  from  other  substances.  Many  of  the  pre- 
cipitates produced  by  potash  exhibit  particular  colour  or 
other  characteristic  properties,  as,  e.  g.  suboxide  of  man- 
ganese, suboxide  of  iron,  suboxide  of  mercury,  and  by 
means  of  these  colours  or  properties  we  may  detect  the  na- 
ture of  the  metals  they  contain.  Potash  expels  ammonia 
from  its  salts,  and  thus  enables  us  to  detect  the  latter  sub- 
stance by  its  odour,  its  reaction  on  vegetable  colours,  &c. 

4-  129. 

7.    CARBONATE    OF    POTASH.       (KO   C02.) 

Preparation.  — Puie  carbonate  of  potash,  for  chemical 
purposes,  is  prepared  by  calcining  purified  bitartrate  of 
potash  in  an  iron  pan,  to  complete  carbonization  ;  the  resi- 
due is  then  boiled  with  water  ;  the  solution  thus  obtained 
is  purified  by  filtration  and  evaporated  to  dryness,  in  a 
clean  iron  pan  ;  towards  the  latter  end  of  this  process  the 
mass  must  be  constantly  stirred.  The  residuary  dry  salt 
is  kept  in  a  well-closed  bottle.  For  use,  one  part  of  it  is 
dissolved  in  five  parts  of  water. 

Testing.  —  Pure  carbonate  of  potash  must  be  perfectly 
white.  Its  solution,  when  supersaturated  with  nitric  acid, 
must  not  be  rendered  turbid  by  chloride  of  barium  nor  by 
nitrate  of  silver ;  and,  when  supersaturated  with  hydro- 
chloric acid  and  evaporated  to  dryness,  must  leave  no  resi- 
due (silica)  when  redissolved  in  water. 

Uses.  —  Carbonate  of  potash  precipitates  all  bases,  with 
the  exception  of  the  alkalies,  most  of  them  as  carbonates, 
but  also  a  few  as  oxides.  Those  bases  which  are  soluble 
in  water,  as  bicarbonates,  are  only  on  boiling  completely 
precipitated  from  their  acid  solutions.  Many  of  the  pre- 
cipitates produced  by  carbonate  of  potash  exhibit  par- 
ticular colours,  and  may  therefore  serve  for  the  detection 
of  the  various  metals.  The  solution  of  carbonate  of  pot- 
ash is  moreover  employed  for  the  decomposition  of  many 
insoluble  salts  with  metallic  bases,  or  bases  of  the  alkaline 
earths,  especially  of  those  with  organic  acids:  For  these 
salts,  on  being  boiled  with  carbonate  of  potash,  are  con- 
verted into  carbonates,  whilst  the  acids  combine  with  the 
potash,  forming  soluble  salts.  Carbonate  of  potash  is  also 


48  AMMONIA. 

used  to  saturate  free  acids,  in  order  to  obtain  them  in  com- 
bination with  potash  as  salts,  and  is,  moreover,  especially 
used  to  precipitate  platinum  from  solutions  containing 
hydrochloric  acid. 

7  ^  •;  - ;  /:"  '.'.«so.  Z  •* '    ! 

8.    AMMONIA.       (NH40.) 

Preparation.  —  Pure  liquor  of  ammonia  is  prepared  by 
slaking  four  parts  of  quick  lime  with  one  and  one-third 
part  of  water,  mixing  this  hydrate  of  lime,  in  a  glass  re- 
tort,- with  five  parts  of  sal  ammoniac  reduced  to  powder, 
and  cautiously  adding  as  much  water  as  will  cause  the 
powder  to  form  into  lumps  when  agitated.  Tfre  retort  is 
then  placed  in  a  sand-bath,  and  brought  into  connexion 
with  two  gas  conducting  tubes,  joined  to  each  other  in  the 
middle  by  means  of  a  rinsing  apparatus,  containing  only  a 
small  quantity  of  water,  such  as  has  been  described  in  the 
preparation  of  sulphuretted  hydrogen,  (vide  $  25r  and  en- 
graving.) The  absorbing  receiver  should  contain  ten 
parts  of  water.  •  This  receiver  is  placed  in  a  vessel  filled 
with  cold  water  j  heat  is  then  applied  to.  the  retort.  The 
evolution  of  gas  immediately  ensues.  The  heat  is  con- 
tinued until  no  more  bubbles  appear,  and  the  stopper  of 
the  retort  is  then  quickly  taken  off,  to  prevent  the  fluid 
from  receding.  The  liquor  of  ammonia  contained  in  the 
washing  apparatus  is  impure,  but  that  in  the  receiver  is 
pure  ;  it  contains  about  sixteen  per  cent,  of  ammonia,  and 
thus  has  a  specific  gravity  of  0.93.  It  is  kept  in  phials 
closed  with  glass  stoppers. 

Testing.  —  Pure  liquor  of  ammonia  must  be  colourless, 
and  upon  evaporation  on  a  watch-glass  not  leave  the  slight- 
est residue.  It  ought  not  to  render  lime-water  turbid, 
(carbonic  acid,)  and  after  supersaturation  with  nitric  acid, 
must  not  be  rendered  turbid  by  solution  of  barytes  nor  by 
solution  of  nitrate  of  silver,  nor  be  coloured  by  sulphu- 
retted hydrogen. 

Uses. — Ammonia  is  one  of  the  most  frequently  used  rea- 
gents. It  is  especially  applied  for  the  saturation  of  acid 
liquids,  for  the  precipitation  of  a  great  many  metallic  ox- 
ides and  earths,  as  well  as  for  their  separation  from  each 


CARBONATE    OF    AMMONIA*  49 

other,  as  many  of  them  are  dissolved  as  ammoniacal  dou- 
ble salts,  by  ammonia  in  excess ;  such  as  the  oxides  of 
zinc,  cadmium,  silver,  copper,  nickel,  and  cobalt,  whilst 
others  remain  insoluble  in  free  ammonia.  The  precipi- 
tates, as  well  as  their  ammoniacal  solutions,  sometimes 
exhibit  a  very  distinct  and  peculiar  colour,  by  means  of 
which  we  may  at  once  detect  the  metals  which  they  con- 
tain. 

Many  oxides  which  are  precipitated  by  ammonia  from 
neutral  solutions,  are  not  precipitated  from  acid  solutions, 
their  precipitation  being  here  prevented  by  the  formation 
of  an  ammoniacal  salt.  (Compare  Chloride  of  Ammonium, 

§  31.      £) 

9.    CARBONATE   OF  AMMONIA.       (NH4O,   CO2.) 

Preparation. — We  use,  for  the  purposes  of  chemical 
analysis,  sesquicarbonate  of  ammonia,  which  must  be  en- 
tirely free  from  any  smell  of  animal  oil,  (such  as  is  pre- 
pared on  a  large  scale,  by  the  sublimation  of  sal  ammoniac 
and  chalk.)  The  outer  and  inner  surface  of  the  mass 
must  be  carefully  scraped  off ;  and  then  one  part  of  the 
salt  dissolved  in  a  mixture  of  four  parts  of  water,  and  one 
part  of  caustic  liquor  of  ammonia. 

Testing. — Pure  carbonate  of  ammonia  must  completely 
evaporate,  and  after  supersaturation  with  nitric  acid,  nei- 
ther be  coloured  nor  precipitated  by  solution  of  barytes, 
nor  by  solution  of  silver,  nor  by  sulphuretted  hydrogen. 

Uses. — Carbonate  of  ammonia  precipitates  most  metal- 
lic oxides  and  earths,  like  carbonate  of  potash.  The  com- 
plete precipitation  of  many  of  them  takes  place  only  on 
boiling.  Several  of  the  precipitated  combinations  redis- 
solve  again  when  this  reagent  is  added  in  excess.  Car- 
bonate of  ammonia  dissolves  many  hydrates  of  oxides  in  a 
like  manner,  and  thus  enables  us  to  separate  them  from 
others  which  are  insoluble.  This  power  of  solution  depends 
upon  the  tendency  of  ammoniacal  salts,  to  form  soluble 
double  salts,  indecomposible  by  free  ammonia  as  well  as 
by  carbonate  of  ammonia. 

Like  caustic  ammonia,  and  for  the  same  reason,  carbon- 


50  CHLORIDE  OF  BARIUM. 

ate  of  ammonia  does  not  precipitate  from  acid  solutions, 
many  oxides  which  it  precipitates  from  neutral  solutions. 
(§  30.)  We  apply  carbonate  of  ammonia,  in  chemical  an- 
alysis, especially  for  the  precipitation  of  barytes,  of  stron- 
tian  and  of  lime,  and  for  the  separation  of  these  substan- 
ces from  magnesia,  as  the  latter  is  not  precipitated  in  the 
presence  of  ammoniacal  salts. 


$  32. 

10.    CHLORIDE    OF    BARIUM.      (Ba,  Cl.) 

Preparation.  —  Six  parts  of  heavy  spar  reduced  to  a  fine 
powder  are  mixed  with  one  part  of  powdered  charcoal 
and  one  and  a  half  part  of  flour  ;  this  mixture  is  put  into 
ahessian  crucible  and  exposed  to  the  strongest  possible 
red  heat.  The  fused  mass  is  rubbed  to  powder  when  cool  ; 
about  nine-tenths  of  the  powder  are  boiled  with  four  times 
their  weight  of  water,  and  hydrochloric  acid  is  added;  un- 
til no  more  effervescence  of  sulphuretted  hydrogen  takes 
place,  and  the  liquid  manifests  an  acid  reaction.  Then 
the  last  tenth  of  the  fused  mixture  is  added,  and  the  boil- 
ing still  continued  for  some  time.  The  alkaline  liquid  is 
then  filtered  and  chrystallized*  The  crystals  when  dry 
are  digested  and  washed  with  alcohol,  redissolved  in  wa- 
ter, and  again  crystallized.  For  use,  one  part  of  the  crys- 
tals is  dissolved  in  ten  parts  of  water. 

Testing.  —  Pure  chloride  of  barium  must  not  affect  veg- 
etable colours,  nor  ought  its  solution  to  be  altered  by  sul- 
phuretted hydrogen,  nor  by  hydrosulphuret  of  ammonia. 
Pure  sulphuric  acid  must  precipitate  every  fixed  particle 
from  it,  so  that  the  filtered  liquid  leaves  not  the  slightest 
residue  when  evaporated  on  a  platinum  plate. 
^  Uses.  —  Barytes  forms,  with  many  acids,  soluble  salts  ; 
with  others,  insoluble  combinations.  This  property  of 
barytes  affords  us  a  means  of  distinguishing  the  former 
acids,  which  are  not  precipitated  by  chloride  of  barium, 
from  the  latter  in  saline  solutions  which  are  precipitated  by 
chloride  of  barium.  These  barytes  precipitates  manifest 
to  other  substances  (acids)  relations  differing  from  each 
other.  Consequently,  by  subjecting  them  to  the  action  of 
such  bodies,  we  may  subdivide  again  the  group  of  precipi- 


NITRATE    OF   BARYTES.        CHLORIDE   OF    CALCIUM.       51 

table  acids,  and  even  directly  detect  certain  acids.  Chlo- 
ride of  barium  is  one  of  our  most  important  reagents,  on 
account  of  its  application  distinguishing  one  group  of  acids 
from  another,  and  especially  as  a  means  of  detecting  sulphu- 
ric acid. 

§  33. 

11.     NITRATE    OF    BARYTES.       (Ba  O,  NO ...  .) 

Preparation. — A  dilute  solution  of  chloride  of  barium 
is  boiled,  and  carbonate  of  ammonia  added,  as  long  as  it 
causes  any  precipitate,  and  further  until  the  liquid  mani- 
fests an  alkaline  reaction.  The  carbonate  of  barytes 
obtained  by  this  process  is  carefully  washed,  and  then  dis- 
solved in  hot  and  dilute  nitric  acid,  until  the  liquid  no 
longer  manifests  any  acid  reaction.  The  solution  is  then 
filtered,  and  afterwards  crystallized  by  evaporation.  One 
part  of  the  crystallized  salt  is  dissolved  in  ten  parts  of 
water,  for  use.  The  tests  as  to  its  purity  are  the  same  as 
in  chloride  of  barium.  Nitrate  of  silver  must  not  render 
its  solution  turbid. 

Uses. — Nitrate  of  barytes  is  analogous  in  its  action  to 
chloride  of  barium,  and  may  be  substituted  for  this  latter 
substance,  when  we  wish  to  avoid  the  formation  of  a 
chloride  in  a  liquid. 

§  34.    "* 

CHLORIDE    OF    CALCIUM.     (Ca  Cl.) 

Preparations. — Chalk  is  added  to  hot  and  dilute  hy- 
drochloric acid,  until  all  acid  reaction  ceases  ;  the  solution 
is  then  filtered,  and,  with  the  addition  of  some  ammonia, 
allowed  to  stand  a  few  hours,  at  a  moderate  heat.  It  is 
then  filtered  again;  the  filtrate  is  heated  to  boiling,  and 
carbonate  of  ammonia  added  until  all  the  lime  is  precipi- 
tated; the  thus  obtained  carbonate  of  lime  is  carefully 
washed.  A  mixture  of  one  part  of  pure  hydrochloric  acid, 
with  five  parts  of  water,  is  then  heated  and  the  washed 
carbonate  of  lime  added  to  complete  neutralization;  the 
solution  is  then  boiled  up  several  times,  filtered,  and  pre- 
served for  use. 

Testing. — Solution  of  chloride  of  calcium  must  be  per- 
fectly neutral,  and  neither  be  tinged  nor  precipitated  by 


52  NITRATE    OF    SILVER. 

hydrosulphuret  of  ammonia ;  nor  ought  it  to  evolve  am- 
monia when  mixed  with  potash  or  with  hydrate  of  lime. 

Use. — Chloride  of  calcium  is,  in  its  action  and  applica- 
tion, analogous  to  chloride  of  barium.  For,  as  the  latter  is 
applied  to  divide  the  inorganic  acids  into  groups,  so  the 
former  serves  for  the  same  purpose  with  the  organic  acids, 
since  it  precipitates  some  of  them,  whilst  it  forms  soluble 
combinations  with  others.  And,  as  is  the  case  with  the 
barytes  precipitates,  the  different  conditions  under  which 
the  various  insoluble  lime  salts  are  precipitated,  furnish  us 
with  means  for  a  more  special  classification  of  these  acids. 

§  35. 

13.     NITRATE    OF    SILVER.    (Ag  0,  N05.) 

Preparation. — To  obtain  nitrate  of  silver  in  a  state  of 
purity,  silver  alloyed  with  copper,  as  e.  g.  a  piece  of 
standard  coin,  is  dissolved  in  nitric  acid.  The  solution  is 
evaporated  to  dryness,  and  the  residue  fused  in  a  small 
porcelain  crucible,  at  a  moderate  heat,  by  means  of  a 
spirit-lamp,  till  all  the  nitrate  of  copper  is  decomposed, 
i.  e.  till  the  green  colour  of  the  salt  has  completely  vanish- 
ed, even  in  the  portions  adhering  to  the  upper  sides  of  the 
crucible,  and  a  portion  dissolved  in  water  becomes  no 
longer  blue  when  ammonia  in  excess  is  added.  The  mass, 
when  cooled,  is  boiled  with  water,  filtered,  and  crystallized. 
One  part  of  the  crystals  is  dissolved  in  twenty  parts  of 
water,  for  use.  The  oxide  of  copper  remaining  after  the 
solution  of  the  fused  mass,  always  contains  some  silver, 
to  remove  which  the  residue  is  dissolved  in  nitric  acid, 
and  the  silver  precipitated  from  the  solution,  as  chloride 
of  silver. 

Testing. — Nitrate  of  silver  may  be  considered  pure,  if 
the  fixed  part  of  its  solution  is  completely  precipitated  by 
dilute  hydrochloric  acid,  so  that  the  fluid  filtered  from  the 
chloride  of  silver  leaves  no  residue  upon  evaporation  on  a 
watch-glass,  and  is  neither  precipitated  nor  tinged  by  sul- 
phuretted hydrogen. 

Use. — Oxide  of  silver  forms,  with  many  acids,  soluble, 
with  others,  insoluble  combinations  ;  nitrate  of  silver  may 


PERCHLORIDE   OF    IRON.  53 

therefore  be  used,  like  chloride  of  barium,  for  the  classifica- 
tion of  acids  into  groups. 

Most  of  the  insoluble  silver  combinations  are  soluble  in 
dilute  nitric  acid,  chloride,  iodide,  bromide,  and  cyanide 
of  silver  excepted.  Nitrate  of  silver  is,  therefore,  an  excel- 
lent means  for  distinguishing  and  separating  the  hydracids 
corresponding  to  the  last-named  silver  combinations  from 
all  other  acids.  Nitrate  of  silver  is  also  of  great  impor- 
tance for  the  detection  of  individual  acids,  as  many  of  the 
silver  precipitates  exhibit  a  particular  colour,  (chromate, 
and  arseniate  of  silver,  for  example,)  or  a  particular  relation 
to  other  reagents,  or  peculiar  properties,  on  being  heated, 
e.  g.  formiate  of  silver. 


§  36. 

14.       PERCHLORIDE    OF    IRON.       (Fe2    C13.) 

Preparation. — To  obtain  pure  perchloride  of  iron,  two 
parts  of  hydrochloric  acid,  diluted  with  from  six  to  eight 
parts  of  water,  are  heated  with  an  excess  of  small  iron 
nails  free  from  rust,  until  the  evolution  of  hydrogen  ceases  ; 
the  solution  is  then  decanted,  mixed  with  one  part  of  hydro- 
chloric acid,  boiled  in  a  very  capacious  vessel,  and,  whilst 
boiling,  nitric  acid  in  small  portions  cautiously  and  gradually 
added,  till  a  further  addition  produces  no  longer  any  effer- 
vescence ;  i.  e.  till  no  more  red  vapours  of  nitrous  acid 
appear,  and  solution  of  ferricyanide  of  potassium  (§  42)  no 
longer  tinges  the  mixture  blue.  A  small  excess  of  nitric 
acid  does  no  harm  whatever.  The  solution  obtained  is 
then  diluted  with  water,  boiled,  ammonia  added  to  alkaline 
reaction,  and  the  produced  precipitate  of  hydrated  peroxide 
of  iron  well  washed  with  hot  water,  and  when  still  moist, 
added  to  a  heated  mixture  of  272  parts  of  hydrochloric 
acid,  and  ten  parts  of  water,  till  the  last  portions  are  not 
dissolved,  even  on  continued  heating.  The  solution  is 
then  filtered,  and  kept  for  use. 

Testing. — Solution  of  perchloride  of  iron,  for  the  pur- 
poses of  chemical  analysis,  must  not  contain  acid  in  excess; 
a  portion  of  it  must,  therefore,  when  stirred  with  a  small 
rod  dipped  in  ammonia,  yield  a  precipitate,  which  is  not 
re-dissolved  on  shaking  the  vessel.  Ferricyanide  of  potas- 
sium must  not  impart  a  blue  tinge  to  it. 


54  PHOSPHATE    OF    SODA. 

Use.  —  Chloride  of  iron  serves  for  a  further  classification 
of  those  organic  acids  which  are  not  precipitated  by  chloride 
of  calcium,  as  it  produces  precipitates  with  benzoic  and 
succinic  salts,  whilst  it  leaves  acetic  and  formic  salts  in 
solution.  The  neutral  salts  which  these  latter  acids  form 
with  peroxide  of  iron,  dissolve  in  water,  imparting  an 
intensely  red  colour  to  the  latter  ;  chloride  of  iron  affords, 
therefore,  a  useful  means  for  their  detection.  (Vide  §  98, 
a  7,  for  its  application  for  the  decomposition  of  phosphates 
of  the  alkaline  earths,  to  which  purpose  it  is  exceedingly 
well  adapted.)  Chloride  of  iron  serves  also  for  the  detec- 
tion of  ferrocyanide  of  hydrogen,  producing  Prussian  blue 
with  this  substance. 

II.  -  SPECIAL  REAGENTS    IN    THE    HUMID    WAY. 

a.  Reagents  which  serve  especially  for  the  detection  or 
separation  of  individual  bases. 


1.    SULPHATE    OF    POTASH.    (KO,   S03.) 

Preparation.  —  The  sulphate  of  potash  of  commerce  is 
purified  by  re-crystallization,  and  one  part  of  the  pure  salt 
is  dissolved  in  twelve  parts  of  water,  for  use. 

Uses.  —  Sulphate  of  potash  precipitates  from  solutions 
of  barytes  and  strontian  the  sulphates  of  the  oxides,  which 
are  insoluble  in  water.  It  serves,  therefore,  for  their  de- 
tection and  separation.  It  also  produces  a  precipitate  in 
very  highly  concentrated  solutions  of  lime,  but,  in  most 
cases,  only  after  the  lapse  of  some  time.  It  does  not  pre- 
cipitate dilute  solution  of  lime.  The  action  of  sulphate  of 
potash  being  analogous  to  that  of  dilute  sulphuric  acid,  it 
is  in  many  cases  preferable  to  the  latter  reagent,  since  it 
does  not  disturb  the  neutrality  of  the  solution. 

§  38.  A, 

2.    PHOSPHATE    OF    SODA.      (2  N<Z  O,  PO5-) 

Preparation.  —  To  obtain  this  reagent  pure,  dilute  com- 


mercial phosphoric  acid  is  heated,  and  solution  of  carbonate 


NEUTRAL  CHROMATE  OF  POTASH.          55 

of  soda  added,  till  all  effervescence  ceases,  and  the  liquid 
manifests  a  feeble  alkaline  reaction.  The  liquid  is  then 
filtered,  evaporated,  and  crystallized.  The  crystals  are 
dried,  triturated  with  a  portion  of  charcoal  and  flour,  and 
the  entire  mass  strongly  heated  in  a  hessian  crucible.  The 
heated  mass  is  then  boiled  with  water,  filtered,  and  crys- 
tallized. One  part  of  the  salt  obtained  is  dissolved  in  ten 
parts  of  water,  for  use.  This  solution  must  not  become 
turbid  on  being  heated  with  ammonia.  The  precipitates 
produced  by  the  addition  of  solution  of  barytes.  and  of 
silver,  must  completely  redissolve  on  the  addition  of  dilute 
nitric  acid. 

Uses. — Phosphate  of  soda  precipitates  the  alkaline 
earths,  and  all  metallic  oxides,  by  double  affinity.  It  serves 
in  the  course  of  analysis,  after  the  separation  of  the  heavy 
metallic  oxides,  as  a  test  for  alkaline  earths  in  general; 
and,  after  the  separation  of  barytes,  strontian,  and  lime, 
with  simultaneous  addition  of  ammonia,  as  a  test  for  the 
detection  of  magnesia,  which  precipitates  under  these  cir- 
cumstances as  basic  phosphate  of  ammonia  and  magnesia. 

§  39.         T~ 

3.     NEUTRAL    CHROMATE    OF   POTASH.     (KO,  Cr  O3.) 

Preparation. — To  obtain  this  reagent  pure,  the  com- 
mercial bichromate  of  potash  is  dissolved  in  water,  and 
carbonate  of  potash  added,  till  the  solution  manifests  a 
feeble  alkaline  reaction.  The  liquid,  which  is  now  of  a 
yellow  colour,  is  then  crystallized.  The  crystals  are  well 
washed  and  re-dissolved  in  water,  in  the  proportion  of  one 
part  of  the  crystals  to  ten  parts  of  water.  The  solution 
must  be  neutral. 

Uses. — Chromate  of  potash  decomposes,  by  double  af- 
finity, most  of  the  soluble  metallic  salts.  The  precipitated 
metallic  chromates  are,  for  the  most  part,  very  difficult  of 
solution,  and  often  manifest  such  peculiar  colourings,  that 
the  metals  they  contain  may  be  easily  detected.  We  use 
chromate  of  potash  principally  as  a  test  for  lead. 


56  CYANIDE    OP   POTASH. 

§   40. 
4.     CYANIDE    OF    POTASSIUM.     (KCy.) 

Preparation. — To  obtain  this  reagent  pure,  commercial 
ferrocyanate  of  potash  is  gently  heated  and  stirred,  till  its 
water  of  crystallization  is  completely  expelled  ;  it  is  then 
pounded,  and  eight  parts  of  the  dry  powder  are  mixed 
with  three  parts  of  perfectly  dry  carbonate  of  potash. 
This  mixture  is  put  into  a  crucible  heated  to  redness,  and 
the  latter  well  closed  and  kept  at  a  bright  red  heat,  till  the 
mass  is  in  a  state  of  clear  and  calnj,  fusion.  The  fused 
cyanide  of  potassium  is  then  poured  into  a  heated  porcelain 
basin ;  this  must  be  done  cautiously,  in  order  to  prevent 
the  passing  over  of  any  particles  of  the  iron  which,  in  a 
highly-divided  state,  has  separated  from  the  mass,  and  sub- 
sided to  the  bottom  of  the  crucible.  The  thus  obtained 
cyanide  of  potassium  is  exceedingly  well  adapted  for 
application  in  analysis,  although  it  contains  cyanate  of 
potash.  It  must  be  perfectly  white.  One  part  is  dissolved 
in  four  parts  of  cold  water. 

Uses. — Cyanide  of  potassium  (containing  cyanate  of  pot- 
ash) produces  in  the  solutions  of  most  metallic  salts  in  wa- 
ter, insoluble  precipitates  of  cyanides,  oxides,  or  carbon- 
ates. The  former  of  these  precipitates  are  soluble  in  cy- 
anide of  potassium  ;  they  may,  therefore,  by  a  further  ad- 
dition of  the  reagent,  be  separated  from  the  oxides,  &c. 
which  are  insoluble  in  cyanide  of  potassium.  Some  of 
the  cyanides  of  metals  always  dissolve  as  cyanides  com- 
bined with  cyanides  of  potassium,  even  if  free  prussic  acid 
be  present;  others  combine  with  cyanogen,  forming 
new  radicals,  and  as  such,  combined  with  potassium,  re- 
main in  solution.  Cobalti-cyanide  of  potassium,  ferro  and 
ferri-cyanide  of  potassium,  are  ihe  most  common  combi- 
nations of  the  latter  kind.  They  differ  from  the  double 
cyanogen  compounds  of  the  former  description,  especially 
inasmuch  as  dilute  acids  do  not  separate  from  them  the 
cyanides  of  metals.  Those  metals  forming  such  com- 
binations may,  therefore,  by  syanide  of  potassium,  be 
separated  from  all  those  metals,  the  cyanides  of  which 
are  precipitated  by  acids,  from  their  Solutions  in  cy- 
anide of  potassium.  This  reagent  has  a  highly  impor- 


FERRICYANIDE   OF  POTASSIUM.  57 

tant  special  application,  in  analysis,  for  the  separation  of 
nickel  from  cobalt. 


5.  FERROCYANIDE    OF    POTASSIUM. 

(C6N3Fe+2K=Cfy+2K.) 

Preparation.  —  Commercial  ferrocyanide  of  potassium 
is  sufficiently  pure  for  the  purposes  of  chemical  analysis. 
One  part  is  dissolved  in  twelve  parts  of  water,  for  use. 

Uses.  —  Ferrocyanide  forms  with  most  metals  combina- 
tions insoluble  in  water,  and  often  very  peculiarly  coloured. 
These  combinations  occur  when  ferrocyanide  of  potassium 
is  brought  into  contact  with  soluble  salts  of  metallic  ox- 
ides, with  chlorides,  &c.  the  potassium  changing  .places 
with  the  metals.  Ferrocyanide  of  copper,  and  ferrocyan- 
ide of  iron,  show  the  most  characteristic  colourings  of  all  ; 
and  ferrocyanide  of  potassium  is,  therefore,  especially  ap- 
plied as  a  reagent  for  the  detection  of  oxide  of  copper 
and  peroxide  of  iron* 

§  42. 

6.  FERRICYANIDE    OF  POTASSIUM. 

(C  12  N6Fe  +3K=2Cfy+3K.) 

Preparation.  —  This  reagent  is  obtained  by  transmitting 
chlorine  gas  through  a  solution  of  one  part  of  ferrocyanide 
of  potassium  in  ten  parts  of  water,  till  a  portion  of  the 
fluid,  when  added  to  a  solution  of  perchloride  of  iron,  no 
longer  produces  a  blue  precipitate,  or  even  a  blue  tinge. 
The  solution  is  then  concentrated  by  evaporation,  and 
some  carbonate  of  potash  added,  until  a  feeble  alkaline  re- 
action becomes  manifest.  The  liquid  is  then  filtered,  and 
allowed  to  cool.  The  crystals  obtained  are  of  a  magnifi- 
cent red  colour.  One  part  is  dissolved  in  ten  parts  of  wa- 
ter, for  use.  The  solution,  as  already  remarked,  must 
neither  produce  a  blue  precipitate  nor  a  blue  tinge,  when 
added  to  solution  of  perchloride  of  iron. 

Uses.  —  Ferricyanide  of  potassium  decomposes  with  so- 
lutions of  metallic  oxides,  in  the  same  manner  as  ferrocy- 
anide of  potassium.  Of  all  ferricyariides  of  metals,  ferri- 


58  HYDROFLUO    SILICIC    ACID. 

cyanide  of  iron  is  peculiarly  characterized  by  its  colour, 
and  we  apply,  therefore,  ferricyanide  of  potassium  espe- 
cially as  a  reagent  for  protoxide  of  iron.  And  for  this  pur- 
pose it  may  very  well  be  prepared  extempore,  by  gradual- 
ly adding  nitric  acid  to  a  solution  of  ferrocyanide  of  potas- 
sium, till  a  portion  of  the  mixture  no  longer  imparts  a  blue 
colour  to  a  solution  of  chloride  of  iron.  All  elevation  of 
temperature  must  be  avoided  in  this  process,  and  the  ves- 
sel ought  to  be  agitated  whilst  the  nitric  acid  is  added. 

§  43. 

7.  HYDROFLUO   SILICIC    ACID.    (3.HF  +  2  Si  F3.) 

Preparation. — This  reagent  is  obtained  in  the  following 
manner  :  equal  parts  of  fluor  spar  and  sand,  in  powder, 
are  mixed  in  a  glass  retort,  with  six  parts  of  English  sul- 
phuric acid ;  the  opening  of  the  retort  is  closed  with  a 
perforated  cork,  into  which  one  end  of  a  double-limbed 
tube  is  fitted  air  tight.  The  exit  limb  must  reach  to  the 
bottom  of  a  flat-bottomed  glass  jar,  and  its  extremity  be 
covered  with  a  column  of  mercury,  to  the  extent  of  a  few 
lines;  this  glass-jar  receiver  contains  four  parts  of  water. 
A  disengagement  of  the  fluo-silicic  gas  immediately  takes 
place,  even  without  the  application  of  heat ;  a  gentle  heat 
by  the  sand-bath  is,  however,  required  to  aid  the  opera- 
tion. Every  bubble  of  gas,  as  it  ascends  through  the  mer- 
cury, produces  a  precipitate  of  hydrate  of  silicic  acid.  One 
equivalent  of  every  threue  equivalents  of* the  fluoride  of  sili- 
con is  decomposed  in  this  process,  and  combines  with 
three  equivalents  of  water,  forming  silicic  acid  which  pre- 
cipitates, and  hydrofluoric  acid,  which  combines  with  the 
two  remaining  equivalents  of  the  fluoride  of  silicon,  form- 
ing hydrofluo  silicic  acid .  The  precipitated  hydrate  of  si- 
licic acid  renders  the  liquid  gelatinous,  and  it  is  on  this 
account  that  the  aperture  of  the  exit  tube  must  be  placed 
under  mercury,  for  it  would  speedily  be  choked  if  this 
precaution  were  neglected.  It  sometimes  happens  in  the 
course,  and  especially  towards  the  end,  of  the  operation, 
that  the  gas  forms  complete  tubes  or  channels  of  silica  in 
the  gelatinous  liquid,  through  which  it  gains  the  surface 
without  decomposition,  if  they  are  not  broken  from  time  to 


OXALIC    ACID..  59 

time  by  stirring.  When  the  disengagement  of  gas  has 
ceased,  the  gelatinous  mass  is  poured  on  a  piece  of  linen, 
and  the  fluid  squeezed  through.  The  liquid  obtained  is 
then  filtered,  and  kept^pr  use.  The  hydrofluo-silicic  acid, 
mixed  with  two  parts  OT  water,  produces  no  precipitate  in 
the  solution  of  salts  of  strontian. 

Uses. — Bases  decompose  with  hydrofluo-silicic  acid, 
forming  water,  and  metallic  fluo-silicates.  Many  of  these 
combinations  are  soluble,  others  insoluble  ;  the  latter  may, 
therefore,  by  means  of  this  reagent,  be  distinguished  from 
the  former.  In  the  course  of  analysis  it  is  only  applied 
for  the  detection  of  barytes. 

§  44. 

8.    OXALIC   ACID.       (2  CO+Or=C2    O3  =  O.) 

Preparation. — This  acid  is  prepared  by  pouring  upon 
one  part  of  starch,  contained  in  a  porcelain  basin,  five 
parts  of  nitric  acid,  of  1.42,  diluted  with  two  parts  of 
water,  and  applying  a  gentle  heat,  till  no  more  nitrous  gas 
is  evolved.  The  liquid  is  then  filtered  and  crystallized  ; 
the  crystals  obtained  are  drained  and  purified  by  a  second 
crystallization.  Oxalic  acid  must  be  preserved  in  the 
form  of  a  powder,  as  it  soon  decomposes  in  solution. 
Pure  oxalic  acid,  when  boiled  with  a  small  quantity  of 
solution  of  indigo,  does  not  discolour  the  latter. 

Uses. — Oxalic  acid  combines  with  many  bases,  forming 
salts  insoluble  in  water  ;  it  may,  therefore,  be  used  to 
precipitate  these  bases.  Many  of  the  oxalates  insoluble 
in  water,  are  easily  dissolved  by  an  excess  of  oxalic  acid, 
whilst  others  dissolve  with  difficulty  in  the  same  men- 
struum. This  relation  affords  us,  therefore,  a  means  of 
distinguishing  the  precipitated  bases  from  each  other. 
As  all  oxalates  insoluble  in  water  are  soluble  in  stronger 
acids,  (hydrochloric  acid,  nitric  acid,)  a  complete  precipi- 
tation by  oxalic  acid  ensues,  in  most  cases,  only  when  the 
liberated  acid  is  saturated  by  an  alkali.  In  analysis, 
oxalic  acid  is  of  great  importance  for  the  detection  and 
precipitation  of  lime. 


60  BITARTRATE    OF    POTASH. 

§    45. 
9.    OXALATE    OF  AMMONIA.       (NH4-fO,  6.) 

Preparation. — This  reagent  il^repared  by  dissolving 
oxalic  acid  in  water,  adding  ammonia  till  a  feeble  alkaline 
reaction  takes  place,  and  crystallising.  One  part  of  the 
salt  is  dissolved  in  twenty -four  parts  of  water,  for  use. 

Uses. —  Oxalate  of  ammonia  is  conveniently  employed 
instead  of  oxalic  acid  and  ammonia.  It  possesses  this 
advantage  over  the  free  acid,  that  its  solution  does  not 
decompose  on  keeping. 

§  46. 

10.    TARTARIC    ACID.     (C  3  H4  O10  =T.) 

The  tartaric  acid  of  commerce  is  sufficiently  pure  for 
the  purposes  of  analysis.*  It  is  best  preserved  in  powder, 
since  it  decomposes  with  the  formation  of  a  white  film 
when  kept  in  solution  for  some  time. 

Uses. — The  addition  of  tartaric  acid  to  solutions  of  iron, 
manganese,  chromium,  alumina,  cobalt,  and  many  other 
metals,  prevents  their  precipitation  by  alkalies,  by  the 
formation  of  double  tartrates  indecbmposible  by  alkalies. 
Tartaric  acid  may,  therefore  be  employed  to  separate  these 
metals  from  others,  the  precipitation  of  which  it  does  not 
prevent.  Tartaric  acid  forms  with  potash,  but  not  with 
soda,  a  bi-salt  difficult  of  solution ;  it  is,  therefore,  one  of 
the  best  means  of  distinguishing  potash  from  soda. 

§  47. 

11.     BITARTRATE    OF    POTASH.     (KO,  HO,  T.) 

The  cream  of  tartar  of  commerce  is  sufficiently  pure 
for  the  purposes  of  qualitative  analysis.  It  should  be  pre- 
served in  powder. 

Uses. — Many  metals  dissolve  in  hot  solution  of  tartar, 
forming  double  tartrates ;  others  do  not.  The  former  may, 
therefore,  by  means  of  this  reagent,  be  separated  from  the 

*  In  cases  where  commercial  salts  are  mentioned,  well-defined 
crystals  should  be  selected. — ED. 


CAUSTIC    BARYTES.  61 

latter.     In  analysis,  tartar  is  employed  in  certain  cases  to 
separate  oxide  of  antimony  from  oxide  of  tin. 

§  48. 

12.    ACETATE    OF    BARYTES.     (Ba  O,  A.) 

Preparation.— This  reagent  is  obtained  in  the  same 
manner  as  nitrate  of  barytes,  (vide  §  33,)  substituting,  of 
course,  acetic  acid  for  the  nitric  acid.  It  may  conveniently 
be  preserved  in  a  dry  state,  as  it  is  but  of  rare  application. 

Uses. — The  acetate  of  barytes  is  employed  to  convert 
sulphates  into  acetates,  (especially  sulphate  of  magnesia, 
and  the  alkaline  sulphates).  As  these  acetates  are  con- 
verted by  heat  into  carbonates,  and  as  carbonate  of  mag- 
nesia is  insoluble,  whilst  the  alkaline  carbonates  are 
soluble  in  water,  acetate  of  barytes  indirectly  serves  to 
separate  magnesia  from  the  alkalies. 

§  49 

13.    CAUSTIC    BARYTES.     (Ba  0.) 

Preparation. — To  prepare  this  reagent,  one  part  of 
sulphuret  of  barium  is  boiled  with  twenty  parts  of  water ; 
copper  scales  are  then  added  in  excess  to  the  solution, 
whilst  boiling,  till  a  filtered  portion  of  the  liquid  ceases  to 
blacken  a  solution  of  acetate  of  lead.  The  solution  is  then 
filtered,  while  still  hot,  and  as  much  water  added  as  will 
prevent  any  considerable  portion  of  the  hydrate  of  barytes 
in  solution  from  crystallizing  on  cooling.  The  saturated 
water  of  barytes  obtained  is  kept  in  well-closed  bottles. 
Should  it  contain  a  small  quantity  of  copper,  some  sul- 
phuretted hydrogen  must  be  cautiously  added,  and  the 
liquid  filtered  from  the  precipitated  sulphuret  of  copper. 

Uses. — Caustic  barytes  is  analogous  in  its  action  to 
potash,  i.  e.  it  precipitates,  as  a  strong  base,  from  saline 
solutions,  those  metallic  oxides  and  earths  which  are  in- 
soluble in  water.  In  analysis,  we  apply  this  reagent  only 
for  the  precipitation  of  magnesia.  For  this  purpose  a 
solution  of  sulphuret  of  barium  may  equally  well  be  em- 
ployed, inasmuch  as  (as  is  generally  the  case)  it  contains 
caustic  barytes.  Water  of  barytes  may  also,  like  the 
3 


62  CHLORIDE   OF 

various  salts  of  barytes,  of  which  we  have  already  treated5, 
be  used  to  precipitate  those  acids  which  form  insoluble 
combinations  with  barytes  ;  we  generally  employ  it  thus 
only  for  the  detection  of  carbonic  acid. 

§  50, 

14,     PROTOCHLORIDE    OF    TIN.     (S?l  CI.) 

Preparation. — To  obtain  this  reagent,  English  tin  is 
reduced  to  powder,  by  being  fused  in  an  iron  spoon,  then 
taken  from  the  fire  and  rubbed  in  a  mortar  till  it  has  re- 
assumed  the  solid  state.  This  powder  is  then,  for  some 
length  of  time,  boiled  with  concentrated  hydrochloric  acid 
in  a  glass  vessel  *  (care  must  always  be  taken  that  the 
mixture  contains  tin  in  excess  ;)  the  solution  is  diluted  with 
four  times  its  quantity  of  water,  slightly  acidulated  with 
hydrochloric  acid,  and  filtered.  The  clear  solution  is  kept 
in  a  small  closed  bottle,  containing  small  pieces  of  metallic 
tin.  If  this  latter  precaution  be  neglected^  the  reagent 
soon  becomes  useless,  the  protochloride  being  converted 
into  perchloride  of  tin. 

Testing. — Pure  protochloride  of  tin,  when  mixed  with 
perchloride  of  mercury,  immediately  produces  a  white 
precipitate  of  protochloride  of  mercury  \  it  yields  a  dark 
brown  precipitate  with  sulphuretted  hydrogen,  and  is 
neither  precipitated  nor  disturbed  by  sulphuric  acid. 

Uses. — The  great  tendency  which  protochloride  of  tin 
has  to  absorb  oxygen,  and  thus  to  form  peroxide  of  tin,  or 
rather  perchloride  of  tin,  as  the  oxide  at  the  moment  of  its 
formation,  unites  with  the  free  hydrochloric  acid  present, 
renders  it  one  of  the  most  powerful  means  of  reduction. 
We  employ  it,  in  analysis,  for  the  detection  of  gold,  for 
which  purpose  it  must  first  be  mixed  with  some  nitric  acid, 
without  the  application  of  heat  j  we  also  use  it  to  detect 
the  presence  of  mercury. 

§  51. 

15.     CHLORIDE    OF    GOLD*     (Au  Cl    .) 

Preparation. — To  obtain  this  reagent,  fine  shreds  of 
gold,  which  may  be  alloyed  either  with  silver  or  with  cop- 


CHLORIDE    OF    PLATINUM.  63 

per,  are  drenched,  in  a  small  retort,  with  aqua  regia  in 
excess,  and  a  gentle  heat  is  applied  till  no  more  gold  is 
dissolved.  If  the  gold  was  alloyed  with  copper,  which  is 
detected  by  the  brown  red  precipitate  produced  by  fer- 
rocyanide  of  potassium,  in  a  portion  of  the  solution  diluted 
with  water,  the  gold  solution  containing  copper  is  mixed 
with  sulphate  of  iron  in  excess.  The  gold  becomes  re- 
duced, and  separates  as  a  fine  brownish  black  powder ;  it 
is  then  washed  in  a  small  retort,  re-dissolved  in  aqua  re- 
gia, the  solution  evaporated  to  dryness  in  the  water-bath, 
and  the  residue  dissolved  in  thirty  parts  of  water.  If  the 
gold  is  alloyed  with  silver,  the  latter  metal  remains  undis- 
s<?lved  as  chloride  of  silver  when  treated  with  aqua  regia. 
In  this  case,  the  first  solution  is  evaporated  to  dryness,  and 
the  residue  dissolved  for  use. 

Uses. — Chloride  of  gold  has  a  great  tendency  to  yield 
its  chlorine  to  other  substances ;  it,  therefore,  easily  converts 
protochlorides  into  perchlorides,  protoxides  into  peroxides 
and  perchlorides,  &c.  These  oxidations  usually  manifest 
themselves  by  the  precipitation  of  pure  metallic  gold,  in  the 
shape  of  a  blackish  brown  powder.  In  analysis,  chloride 
of  gold  serves  only  for  the  detection  of  protoxide  of  tin,  as 
it  produces  a  purple  colour  or  precipitate  in  solutions  con- 
taining this  substance.  (Vide  infra.) 

552. 

16,     CHLORIDE    OF    PLATINUM>    (Pt  C12.) 

Preparation. — To  obtain  this  reagent,  platinum  in  pow- 
der is  boiled  with  nitric  acid,  for  the  purpose  of  purifica- 
tion, and  then,  in  a  retort  with  narrow  neck,  drenched  with 
concentrated  hydrochloric  acid,  and  some  nitric  acid ;  a 
gentle  heat  is  applied,  and,  from  time  to  time,  some  nitric 
acid  added,  until  all  the  platinum  is  dissolved.  The  solu- 
tion is,  with  the  addition  of  hydrochloric  acid,  evaporated 
to  dryness  by  a  water-bath,  and  the  residue  dissolved  in 
ten  parts  of  water. 

Uses. — Chloride  of  platinum  forms  very  sparingly  solu- 
ble double  salts,  with  chloride  of  potassium  and  hydro- 
chlorate  of  ammonia,  whilst  it  enters  into  no  such  combina- 
tions with  chloride  of  sodium.  It  serves,  therefore,  to 


64  ZINC*    more. 

detect  ammonia  and  potash,  and  is,  indeed,  for  the  latter 
substance,  nearly  the  most  susceptible  reagent  we  possess. 


17.  ZINC.     (Zn.) 

• 

Pure,  sublimed  zinc,  is  selected  for  the  purposes  of  che- 
mical analysis  ;  it  must  especially  be  free  from  arsenic. 
The  method  described  in  §  24  may  be  employed  as  a  test 
to  detect  the  presence  of  any  trace  of  this  latter  substance. 
The  pure  zinc  should  be  fused,  and  a  portion  of  it  gradu- 
ally dropped  into  a  large  vessel,  containing  water;  the 
remainder  should  be  poured  into  wooden  moulds,  coated 
with  chalk,  for  the  purpose  of  casting  it  into  little  cylin- 
ders. 

Uses.  —  Zinc  precipitates  many  metals  in  their  metallic 
state,  by  depriving  them  of  their  oxygen  and  acid,  owing 
to  the  great  affinity  it  possesses  for  oxygen,  and  its  oxide 
for  acids.  As  the  precipitated  metals  vary  in  colour,  form, 
&c.,  zinc  may  serve  as  well  for  their  detection  and  dis- 
tinction from  each  other,  as  for  their  precipitation.  We 
employ  it  especially  for  the  precipitation  of  antimony  and 
of  tin.  Zinc  is  also  frequently  used  for  the  production  of 
hydrogen. 

§  54.  ^ 

18.    IRON.    (Fe.) 

Iron,  like  zinc,  reduces  many  metals,  and  precipitates 
them  in  a  pure  state.  We  employ  it  especially  for  the  de- 
tection of  copper,  which  is  precipitated  on  it  with  its  cha- 
racteristic colour.  All  clean  surfaces  of  iron,  such  as 
knife-blades,  needles,  pieces  of  wire,  &c.,  are  well  adapted 
to  this  purpose. 

§  55. 
19.  COPPER.  (Cu.) 

We  employ  copper  exclusively  for  the  reduction  of  mer- 
cury, which  precipitates  thereon  as  a  white  coating,  which 


ACETATE    OP   POTASH.      CAUSTIC    LIME.  65 

shines  with  silvery  lustre  when  rubbed.  Any  copper  coin 
scoured  with  fine  sand,  in  fact,  any  clean  copper  surface, 
may  be  employed  for  this  purpose. 

b.  Special  reagents  which  are  particularly  employed  for 
the  detection  and  separation  of  acids. 

§  56. 

1.    ACETATE    OF    POTASH.      (KO,  A.) 

Preparation. — This  reagent  is  obtained  by  dissolving 
one  part  of  pure  carbonate  of  potash  in  two  parts  of  water, 
heating  the  solution  and  exactly  saturating  with  acetic  acid. 

Uses. — Every  salt  of  potash  may  serve  to  produce  a 
precipitate  of  tartar,  and,  therefore,  to  detect  tartaric  acid. 
But  the  acetate  of  potash  is  peculiarly  adapted  for  this 
purpose,  as  the  precipitated  tartar  is  insoluble  in  the  lib- 
erated acetic  acid.  As  this  test  is  rarely  employed,  it  is 
best  to  prepare  it  when  needed. 

§  57. 

2.    CAUSTIC    LIME.    (Ca.  0.) 

Newly  prepared  hydrate  of  lime  is  agitated  and  digested 
for  some  time  in  cold  distilled  water,  allowed  to  settle, 
and  the  clear  fluid  decanted  and  kept  in  well-closed  bot- 
tles. Lime-water  must  impart  a  bright  green  tinge  to 
Georgina  paper,  and  yield  with  carbonate  of  potash  no  in- 
considerable precipitate.  It  becomes  useless  as  soon  as 
it  no  longer  manifests  these  properties,  which  soon  takes 
place  when  it  is  exposed  to  the  access  of  air.  Besides 
lime-water,  hydrate  of  lime  also  ought  to  be  kept  at  hand. 

Uses. — Lime  forms  with  some  acids  insoluble,  with 
others,  soluble  salts.  Lime-water  may,  therefore,  be  em- 
ployed to  distinguish  these  acids  from  each  other,  as  it  pre- 
cipitates the  former  whilst  it  yields  no  precipitate  with  the 
latter.  Many  of  the  precipitable  acids  are  precipitated 
only  under  certain  conditions,  as  e.  g.  on  boiling,  (citric 
acid ; )  and  it  is  therefore  easy  to  distinguish  them  from 
each  other  by  altering  these  conditions.  We  employ  lime- 
water  especially  for  the  detection  of  carbonic  acid,  and  to 


66  CHLORIDE    OF  MAGNESIUM. 

distinguish  from  each  other  paratartaric  acid,  tartaric  acid, 
and  citric  acid.  Hydrate  of  lime  serves,  like  caustic  potash, 
to  liberate  ammonia,  and  is  in  many  cases  preferable  to 
the  latter  reagent. 

§  58. 

3.    SULPHATE  OF  LIME.       (CaO,  S03.) 

Preparation. — To  obtain  this  reagent,  a  concentrated  so- 
lution of  chloride  of  calcium  is  mixed  with  dilute  sulphuric 
acid ;  the  precipitate  produced  is  well  washed,  digested, 
and  for  some  time  agitated  with  water,  then  allowed  to 
settle,  and  the  clear  fluid  decanted  and  kept  for  use. 

Uses. — Sulphate  of  lime  serves  for  the  further  subdi- 
vision of  those  acids  which  are  precipitable  by  chloride  of 
calcium,  as,  owing  to  its  difficult  solubility,  a  few  acids 
only  of  that  group  (oxalic  acid,  paratartaric  acid,)  cause 
precipitates  in  its  solution.  The  solution  of  sulphate  of 
lime  serves,  moreover,  as  a  reagent  for  bases,  viz.,  to  distin- 
guish barytes,  strontian,  and  lime  from  each  other.  For, 
of  course,  it  cannot  precipitate  the  latter,  whilst  it  behaves 
with  solutions  of  barytes  and  of  strontian,  in  the  same 
manner  as  highly  dilute  sulphuric  acid,  i.  e.  it  precipitates 
barytes  immediately,  and  strontian  only  after  the  lapse  of 
some  time. 

§  59. 

4.  CHLORIDE    OF    MAGNESIUM.      (Mg.  Cl.) 

Preparation.  —  Chloride  of  magnesium  is  prepared  by 
heating  a  mixture  of  one  part  of  hydrochloric  acid  and  two 
and  a  half  parts  of  water,  and  adding  basic  carbonate  of 
magnesia,  (magnesias  carbonas  of  the  shops,)  till  the  liquid 
ceases  to  manifest  any  acid  reaction.  The  solution  is  once 
more  boiled  up,  filtered,  and  kept  for  use.  Sulphate  of 
magnesia  may,  in  most  cases,  be  substituted  for  chloride  of 
magnesium. 

Uses. — Chloride  of  magnesium  almost  exclusively  serves 
for  the  detection  of  phosphoric  acid,  as  it  precipitates  from 
the  aqueous  solutions  of  phosphates,  with  presence  of  am- 
monia, a  double  salt,  (basic  phosphate  of  magnesia  and 


NEUTRAL    ASCETATE    OF     LEAD.  67 

ammonia,)  which  is  almost  insoluble  and  highly  character- 
istic in  its  properties.  Chloride  of  magnesium  is,  more- 
over, employed  as  a  test  of  the  purity  of  hydros ulphuret  of 
ammonia.  (Vide  §  26.) 

§  6(X 

5.    PROTO-SULPHATE    OF    IRON.       (Fe  O,  SQ3.) 

Preparation. — To  obtain  this  reagent,  a  quantity  of 
iron  nails,  (free  from  rust,)  in  excess,  is  heated  with  dilute 
sulphuric  acid  till  no  more  hydrogen  is  evolved ;  the  so- 
lution is  then  filtered,  and  after  the  addition  of  a  few  drops 
©f  dilute  sulphuric  acid,  left  to  cool.  Crystals  are  imme- 
diately obtained,  if  the  solution  was  sufficiently  concentra- 
ted, but  if  more  dilute,  evaporation  must  be  had  recourse  to. 
The  crystals  are  washed  with  water  slightly  acidulated 
with  sulphuric  acid,  dried  and  preserved. 

Uses. — Proto-sulphate  of  iron  has  a  great,  disposition  to 
change  to  persulphate  of  iron,  i.  e.  to  absorb  oxygen.  It 
acts,  therefore,  as  a  powerful  means  of  reduction.  We 
employ  it  especially  for  the  reduction  of  nitric  acid,  from 
which  it  separates  nitric  oxide,  by  depriving  it  of  three 
-atoms  of  oxygen.  As  this  decomposition  is  attended  with 
the  formation  of  a  characteristic,  intensely  brownish-black 
coloured  combination  of  nitric  oxide  with  undecomposed 
protosulphate  of  iron,  this  reaction  is  particularly  charac- 
teristic and  susceptible  for  the  detection  of  nitric  acid. 
Protosulphate  of  iron  serves,  moreover,  for  the  detection  of 
ferricyanide  of  hydrogen,  with  which  it  produces  a  kind  of 
Prussian  blue,  and  for  the  detection  of  gold,  which  it  preci- 
pitates from  its  solutions  in  its  metallic  state, 

NEUTRAL  ACETATE  OF  LEAD. 

$  61. 

6.    SOLUTION  OF  MAGNETIC  OXIDE  OF  IRON  (FERROSO-FERRIC 

OXIDE.)  (FeO,  Fe2O3.) 

This  reagent  is  not  kept  on  hand,  but  prepared,  when 
needed,  by  mixing  solution  of  protosulphate  of  iron  with 
some  perchloride  of  iron,  (Fe  0,  SO  +Fe2Cl  .)  It 


6S  BASIC  ACETATE    OF  LEAD. 

serves  for  the  detection  of  hydrocyanic  acid,  which,  when 
previously  combined  with  alkalies,  yields  with  it  a  precipi- 
tate of  sesquiferrocyanide  of  iron  (Prussian  blue.) 

§  62. 

7.    OXIDE  OF  LEAD.       (Pb  O.) 

Oxide  of  lead  is  employed  for  the  detection  of  free  acetic 
acid,  as  it  forms  with  no  other  acid  than  this,  a  soluble 
combination  with  an  alkaline  reaction.  Finely- washed 
litharge  answers  this  purpose  sufficiently  well.  (Compare 
§104,  a.) 

V,         v  §63.       \ 

8.  NEUTRAL  ACETATE  OF  LEAD.   (Pb  O,  A.) 

The  better  sorts  of  commercial  acetate  of  lead  are  suffi- 
ciently pure  for  the  purposes  of  chemical  analysis.  One 
part  is  dissolved  in  ten  parts  of  water  for  use. 

Uses. — Oxide  of  lead  forms,  with  a  great  many  acids, 
combinations  which  are  insoluble  in  water,  and  are  distin- 
guished by  their  colour,  or  by  some  characteristic  property. 
The  acetate  of  lead  produces,  therefore,  precipitates  in 
solutions  of  these  acids  or  their  salts,  and  essentially  con- 
tributes to  ascertain  and  characterize  several  of  them. 
Thus,  in  particular,  chromate  of  lead  is  distinguished  by 
its  yellow  colour,  phosphate  of  lead  by  its  peculiar  relation 
before  the  blow-pipe,  and  malate  of  lead  by  its  easy 
fusibility* 

§64. 

BASIC  ACETATE  OF  LEAD.       (3PbO,  A.) 

Preparation. — This  reagent  is  obtained  by  drenching  in 
a  well-stopped  bottle,  seven  parts  of  finely-washed  litharge, 
and  six  parts  of  neutral  acetate  of  lead,  with  thirty  parts  of 
water,  and  allowing  them  to  stand  at  a  moderate  heat,  shak- 
ing it  from  time  to  time,  till  the  sediment  in  it  has  become 
perfectly  white.  The  clear  fluid  is  then  decanted  and  pre- 
served in  a  well-stopped  bottle.  This  acetate  of  lead  is  un- 
fit for  use,  if  it  contains  copper,  which  is  detected  by  the 


HYDRATED   OXIDE  OF    BISMUTH.  69 

blue  colour  it  exhibits  on  the  addition  of  ammonia.  It  must, 
in  this  case,  be  purified  by  digesting  it  with  metallic  lead, 
till  all  the  copper  is  precipitated. 

Uses. — The  basic  acetate  of  lead,  like  the  neutral  ace- 
tate, precipitates  those  acids  which  form  insoluble  combi- 
nations with  oxide  of  lead,  and,  indeed,  all  those  soluble  in 
acetic  acid,  more  completely  than  the  former  reagent.  We 
employ  it  in  analysis  especially  for  the  detection  of  sulphu- 
retted hydrogen,  for  which  substance  at  is  nearly  the  most 
susceptible  reagent.  It  serves,  moreover,  to  neutralize  free 
acids,  in  cases  where  it  is  desirable  to  avoid  the  application 
of  an  alkali,  e.  g.  to  render  solutions  of  highly*  acid  nitrate 
of  bismuth  precipitable  by  water. 

§  65. 

HYDRATED   OXIDE  OF  BISMUTH.       (Bi  O  +  HO.) 

Preparation. — Bismuth  reduced  to  a  gross  powder  is 
projected  into  pure  nitric  acid,  1,  2  as  long  as  solution 
takes  place  ;  this  prpcess  may  be  promoted  by  the  appli- 
cation of  a  gentle  heat.  The  solution  obtained  is  diluted 
with  about  an  equal  quantity  of  warm  water,  (slightly  acidi- 
fied writh  nitric  acid,)  and  then  filtered ;  the  filtrate  is  mixed 
with  from  ten  to  twenty  parts  of  water,  and  ammonia  added 
to  the  milky  fluid,  till  the  reaction  becomes  perceptibly  alka- 
line; the  solution  is  then  heated,  and  the  precipitate  obtained 
washed,  first,  by  decanting  the  supernatant  liquid,  and  then 
rinsing  the  precipitate  upon  a  filter,  and  afterwards  drying 
it  between  some  sheets  of  blotting-paper,  at  a  moderate 
heat. 

Uses. — The  oxide  of  bismuth,  when  boiled  with  alkaline 
solutions  of  sulphurets,  decomposes  with  the  latter,  giving 
rise  to  the  formation  of  metallic  oxides,  (corresponding 
with  the  various  degrees  of  sulphuration  of  the  sulphurets,) 
and  of  sulphuret  of  bismuth.  It  affords  us,  therefore, 
especially,  a  very  proper  and  efficient  means,  to  convert 
the  sulphuret  or  bisulphuret  of  arsenic  into  arsenious  or 
arsenic  acid. 


70  PROTONITRATE    OF    MERCURY. 

§    66. 
SULPHATE    OF    COPPER.       (Cll  O,  SO3.) 

Preparation. — The  blue  vitriol  of  commerce  may  be 
purified  by  repeated  recrystallization. 

Uses. — Sulphate  of  copper  is  employed  in  qualitative 
analysis,  for  the  precipitation  of  hydriodic  acid,  as  protio- 
dide  of  copper.  For  this  purpose  a  solution  of  one  part 
of  the  blue  vitriol  must  be  mixed  with  two  and  a  quarter 
parts  of  protosulphate  of  iron,  or  else  half  of  the  iodine  will 
separate  in  #  free  state.  The  protoxide  of  iron,  in  this 
process,  changes  to  peroxide,  by  reducing  the  peroxide  of 
copper  to  protoxide.  Sulphate  of  copper  is  besides  used 
as  a  test  for  the  detection  of  arsenious  and  arsenic  acid, 
and  it  is,  indeed,  as  such  very  susceptible,  but  by  no  means 
characteristic.  For  this  purpose  it  is  best  to  prepare  am- 
monio- sulphate  of  copper  by  adding  ammonia  to  a  solution 
of  sulphate  of  copper  till  the  precipitate  which  appears  at 
first,  is  redissolved.  We  refer  to  §  94,  d.  6,  for  the  man- 
ner in  which  sulphate  of  copper  is  employed,  in  junction 
with  caustic  potash,  to  detect  arsenious  acid,  and  especially 
to  distinguish  it  from  arsenic  acid.  Sulphate  of  copper 
may,  moreover,  be  employed  for  the  detection  of  ferrocy- 
anide  of  hydrogen. 

§  67. 

12.    PROTONITRATE    OF    MERCURY.       (Hg2    O,  N05.) 

Preparation. — To  prepare  this  reagent,  nine  parts  of 
nitric  acid,  of  1.23,  are  gently  heated  in  a  small  retort, 
with  ten  parts  of  mercury,  till  no  more  red  vapour  of  ni- 
trous acid  appear ;  the  solution  is  then  boiled  for  some 
time  with  the  undissolved  metallic  mercury,  taking  care  to 
replace  the  water  lost  by  evaporation,  till  a  solution  of  com- 
mon salt  in  excess  precipitates  from  a  portion  of  the  liquid, 
all  the  mercury  it  contains,  as  a  protochloride,  so  that  pro- 
tochloride  of  zinc  produces  no  precipitate  in  the  filtered 
liquid.  The  original  solution  is  then  shaken  until  cold ; 
the  crystals  obtained  are  pounded,  and  agitated  with 
twenty  parts  of  cold  water,  to  which  a  very  small  quantity 


AMMONIO-NITRATE  OF   SILVER.  71 

of  nitric  acid  is  added.     The  solution  is  then  filtered,  if 
necessary,  and  kept  in  a  glass  bottle,  the  bottom  of  which 
is  covered  with  mercury. 

Uses,  —  The  protonitrate  of  mercury  acts  in  a  manner 
analogous  to  the  corresponding  salt  of  silver.  In  the  first 
place,  it  precipitates  many  acids,  especially  the  hydracids  ; 
and  2,  it  serves  for  the  detection  of  several  substances  of 
easy  oxidation,  e.  g.  of  formic  acid,  since  their  oxidation  at 
the  expense  of  the  oxygen  of  the  black  oxide  of  mercury, 
is  attended  by  the  highly  characteristic  precipitation  of  me- 
tallic mercury. 

§  68. 

13.    PEROXIDE    OF    MERCURY.      {Hg  O.)          ^ 

The  peroxide  of  mercury  of  commerce  is  reduced  to  a 
fine  powder,  after  having  been  moistened  with  some  alco- 
hol, in  order  to  prevent  its  minute  particles  from  rising  into 
the  air.  This  powder  is  then  kept  for  use.  As  a  reagent 
it  affords  us  a  certain  means  of  detecting  hydrocyanic  acid, 
since  it  dissolves  in  an  alkaline  fluid  only  when  this  acid 
is  present  (Compare  §  100,  d.) 

§  69, 

14-       PERCHLORIDE    OF   MERCURY,       (Hg  Cl.) 

The  commercial  perchloride  of  mercury  is  sufficiently 
pure  for  the  purposes  of  chemical  analysis.  For  use,  one 
part  is  dissolved  in  sixteen  parts  of  water. 

Uses. — Perchloride  of  mercury  yields  with  various 
acids,  e.  g.  with  hydriodic  acid,  precipitates  of  the  charac- 
teristic colour,  but  it  is,  nevertheless,  one  of  the  less  essen- 
tial reagents  for  the  determination  of  acids.  It  acts,  more- 
over, as  a  means  of  oxidation,  and  allows  us  to  detect  the 
presence  of  easily  oxidizable  bodies,  e.  g.  of  protoxide  of 
tin,  by  the  precipitation  of  protochloride  of  mercury, 

§  70. 

AMMONIO-NITRATE  OF    SILVER.      (Ag   O,  NO  5    +  SNHs.) 

This  reagent  is  not  kept  on  hand,  but  prepared,  when 


72  SUPHUROTJS    ACID.       CHLORINE. 

needed  for  use,  by  cautiously  dropping  caustic  ammonia 
into  a  solution  of  nitrate  of  silver,  till  the  precipitate  which 
at  first  appears  is  re-dissolved.  It  serves  for  the  detection 
of  arsenious  and  arsenic  acid  in  solutions  which  contain  a 
free  acid. 

§  71. 

SULPHUROUS   ACID.       (S02.) 

Preparation. — To  obtain  this  acid,  small  pieces  of  char- 
coal are  heated  in  a  retort  with  six  or  eight  times  their 
•weight  of  English  sulphuric  acid,  and  the  evolved  gas  is 
transmitted  through  water  (which  must  be  kept  cool)  till 
no  more  sulphurous  acid  is  absorbed.  The  solution  obtained 
nius4  be  kept  in  well-closed  bottles. 

Uses. — Sulphurous  acid  has  a  great  disposition  to  be 
converted  into  sulphuric  acid,  by  the  absorption  of  oxygen. 
It  is,  therefore,  one  of  our  most  powerful  means  of  reduc- 
tion; it  precipitates  metallic  mercury  from  its  solutions, 
and  converts  chromic  acid  into  oxide  of  chromium,  in  the 
same  manner  as  protochloride  of  tin.  We  employ  sul- 
phurous acid  principally  for  the  conversion  of  arsenic  acid 
into  arsenious  acid,  in  order  to  be  enabled  to  precipitate 
arsenic  more  rapidly  and  more  completely,  by  means  of 
sulphuretted  hydrogen.  (Vide  §  93,  e.)  Before  applying 
this  reagent,  it  is  always  necessary  to  ascertain  byjts 
odour  whether  it  has  undergone  decomposition. 

§  72. 

17.  CHLORINE.     (Cl.) 

Preparation.  —  One  part  of  pounded  peroxide  of  manga- 
nese is  drenched  in  a  retort,  with  from  four  to  five  parts 
of  commercial  hydrochloric  acid  ;  a  gentle  heat  is  then 
applied  to  the  retort,  and  the  evolved  gas  is  conducted  into 
a  jar  containing  about  from  thirty  to  forty  parts  of  water  at 
the  lowest  possible  temperature*  The  chlorine  water  ob- 
tained must  be  kept  in  a  well  closed  bottle,  and  cautiously 
protected  from  the  influence  of  light,  for  if  this  precaution 
be  neglected,  it  will  soon  become  completely  decomposed, 
i.  e.  converted  into  dilute  hydrochloric  acid,  with  evolution 
of  oxygen,  (owing  to  the  decomposition  of  the  water.) 


SOLUTION   OF    INDIGO.       STARCH-PASTE.  73 

Uses. — Chlorine  has  a  greater  affinity  for  metals  and 
for  hydrogen  than  iodine  and  bromine.  Chlorine  water  is, 
therefore,  an  efficient  means  of  expelling  iodine  and  bromine 
from  their  combinations.  Free  chlorine  forms  with  bromine 
chloride  of  bromine,  and  with  iodine,  chloride  of  iodine, 
and  these  combinations  present  a  different  relation  to  that 
of  the  uncombined  metalloids  ;  we  must,  therefore,  in  cer- 
tain cases,  e.  g.  when  testing  for  iodine  by  means  of 
starch,  (§  100,)  carefully  avoid  adding  chlorine  water  in  ex- 
cess. Chlorine  serves,  moreover,  for  the  destruction  of 
organic  substances,  by  depriving  water,  which  contains 
these  substances,  of  its  hydrogen,  so  that  the  liberated 
oxygen  is  enabled  to  combine  with  the  vegetable  elements, 
and  thus  to  effect  their  decomposition.  For  this  latter 
purpose  it  is  most  advisable  to  evolve  chlorine  in  the  fluid 
which  contains  the  organic  substances,  by  adding  hydro- 
chloric acid  to  it,  heating  it  to  boiling,  and  then  adding 
chlorate  of  potash.  In  this  process  chloride  of  potassium 
and  water  are  formed,  and  chlorous  acid  and  chlorine 
liberated. 

§  73. 

18*    SOLUTION   OF    INDIGO. 

Preparation. — One  part  of  pounded  indigo  is  heated 
with  seven  parts  of  fuming  sulphuric  acid.  The  solution 
obtained  is  diluted  for  use,  with  so  much  water  that  the 
fluid  just  appears  still  distinctly  blue, 

Uses. — Indigo  becomes  decomposed  when  boiled  with 
nitric  acid,  giving  rise  to  the  formation  of  oxidation-pro- 
ducts of  a  yellow  colour.  It  is,  therefore,  employed  for 
the  detection  of  nitric  acid,  either  in  its  free  and  uncom- 
bined state  or  in  its  salts ;  in  which  latter  case,  however, 
the  nitric  acid  must  first  be  liberated  by  means  of  sul- 
phuric acid. 

§74. 

19.     STARCH-PASTE. 

Common  starch  is  rubbed  with  cold  water,  and  the  mix- 
ture then  heated  to  the  boiling  point,  being  at  the  same 
time  constantly  stirred.  The  paste  must  be  uniform,  and 
so  thin  as  almost  to  run. 


74  MIXTURE    OF  SODA,    &C. 

Uses.  —  Starch,  when  brought  into  contact  with  free 
iodine,  forms,  with  this  latter  substance,  a  peculiar  dark- 
blue  combination,  the  colour  of  which  is  so  intense  that  it 
is  distinctly  perceptible,  even  when  the  two  substances 
are  brought  together,  in  a  highly  dilute  state.  Starch- 
paste  is,  therefore,  a  most  excellent  and  delicate  test  for 
free  iodine.  It  is  by  far  less  susceptible  with  regard  to 
bromine,  as  the  fiery  yellow  colour  of  bromide  of  starch  is 
far  less  characteristic  and  intense  than  that  of  iodide  of 
starch. 

B.    REAGENTS  IN  THE  DRY  WAY. 

1.  Fluxes  and  means  of  decomposition. 

§  75. 

1.    MIXTURE    OF    CARBONATE    OF  SODA   AND    CARBONATE   OF 
POTASH. 

(NaO,  CO2+KO,  C02.) 

Preparation. — Ten  parts  of  dried  carbonate  of  soda  are 
rubbed  together  with  thirteen  parts  of  dry  carbonate  of 
potash ;  the  mixture  is  kept  in  a  closed  vessel. 

Uses.-*— When  silicic  acid  or  silicates  are  fused  with 
about  four  parts,  (and  consequently  with  an  excess,)  of 
carbonate  of  potash  or  soda,  a  basic  alkaline  silicate  is 
formed,  (carbonic  acid  escaping  with  effervescence,)  which, 
being  a  combination  soluble  in  water,  may  be  separated 
from  such  metallic  oxides  as  it  may  peradventure  contain, 
and  from  which  hydrochloric  acid  always  separates  silicic 
acid  in  its  soluble  modification.  When  a  fixed  alkaline 
carbonate  is  fused  together  with  sulphate  of  barytes,  of 
strontia,  or  of  lime,  carbonates  of  the  alkaline  earths  and 
sulphate  of  the  alkali  present  are  formed,  in  which  com- 
binations the  base,  as  well  as  the  acid  of  the  previously 
insoluble  salts,  may  now  be  ascertained  with  facility.  In 
order  to  enable  us  to  render  soluble  the  insoluble  silicates 
and  sulphates,  we  use  neither  carbonate  of  potash  nor 
carbonate  of  soda,  separately,  but  the  above  mixture  of 
both,  because  this  mixture  requires  a  far  lower  degree  of 
heat  for  fusion  than  either  of  its  components,  and  thus 


CARBONATE  OF  BARYTES.   NITRATE  OF  POTASH.    75 

renders  it  possible  to  conduct  the  operation  over  a  Ber- 
zelius  lamp.  This  should  always  be  done  in  a  platinum 
crucible,  when  no  easily  reducible  metallic  oxides  are 
present. 

§  76. 

2.  CARBONATE  OF  BARYTES.   (Ba  O,  CO2.) 

For  the  preparation  of  this  reagent  we  refer  the  reader 
to  §  33. 

Uses. — When  silicates  are  heated  with  about  six  times 
their  weight  of  carbonate  of  barytes  till  they  begin  to  fuse 
together,  the  silicates  decompose  with  the  salt  of  barytes, 
in  the  same  manner  as  with  alkaline  carbonates,  i.  e.  su- 
perbasic  silicate  of  barytes  is  formed,  which  is  easily  de- 
composed by  hydrochloric  acid,  the  carbonic  acid  escapes 
and  the  oxides  separate.  It  is,  however,  by  far  more  dif- 
ficult to  render  silicates  completely  soluble  by  this  method, 
than  by  means  of  alkaline  carbonates ;  and  we  use  car- 
bonate of  barytes,  therefore,  only,  when  we  intend  to  test 
silicates  as  to  the  presence  of  alkalies.  The  operation 
with  carbonate  of  barytes  is  conducted  in  a  platinum 
crucible. 

§77. 

3.    NITRATE    OF    POTASH.       (KO,  Nofi.) 

Preparation. — Commercial  saltpetre  is  dissolved  to 
saturation  in  boiling  water.  The  solution  is  then  diluted 
with  a  small  quantity  of  water,  filtered  hot  into  a  glass 
beaker  ;  this  latter  put  into  cold  water,  and  the  solution 
stirred  till  cold.  The  crystalline  powder  obtained  is 
thrown  on  a  filter  and  washed  with  cold  water  till  the 
filtrate  is  no  longer  disturbed  by  nitrate  of  silver.  It  is 
then  well  dried  and  kept  for  use. 

Testing. — A  solution  of  pure  nitrate  of  potash  must 
neither  be  disturbed  by  solution  of  silver,  nor  by  solution 
of  barytes,  nor  precipitated  by  carbonate  of  potash. 

Uses. — Saltpetre  serves  as  a  very  powerful  means  of 
oxidation,  by  yielding  oxygen  to  combustible  substances 


76  CHARCOAL. 

when  heated  with  them.  We  use  it  principally  to  convert 
several  metallic  sulphurets,  especially  the  sulphurets  of 
tin,  of  antimony,  and  of  arsenic,  into  oxides  and  acids  ;  and 
also  for  the  rapid  and  complete  combustion  of  organic 
bodies.  For  this  latter  purpose,  however,  nitrate  of  am  - 
monia  is,  in  most  cases,  preferable  :  we  obtain  this  by  sa- 
turating nitric  acid  with  carbonate  of  ammonia. 

II.    BLOW-PIPE    REAGENTS. 

§  78. 

1.    CHARCOAL.       (C.) 

Any  kind  of  completely  calcined  -wood  charcoal  may  be 
used  for  blow-pipe  experiments.  The  charcoal  of  pine  or 
linden-wood  is,  however,  preferable  to  any  other  sort. 
Smooth  pieces  ought  to  be  selected,  as  knotty  pieces  split 
and  throw  off  fragments  of  the  test  specimen  when  heated. 

Uses. — Charcoal  is  principally  used  as  a  support  for 
the  matter  under  examination  in  blow-pipe  experi- 
ments, (vide  §  12.)  The  following  are  the  properties 
which  render  it  so  valuable  in  this  respect.  First,  its  infu- 
sibility ;  2d,  its  low  conducting  power  for  heat,  which 
admits  of  a  substance  being  heated  more  strongly  upon  a 
charcoal  than  on  any  other  support ;  3d,  its  porosity,  by 
means  of  which  it  imbibes  easily  fusible  substances,  such 
as  borax,  soda,  &c.,  whilst  infusible  bodies  remain  on  its 
surface  ;  4th,  its  property  of  reducing  oxidized  bodies,  by 
means  of  which  it  co-operates  in  the  reduction  of  oxides  by 
the  inner  flame  of  the  blow-pipe.  Charcoal  serves,  more- 
over, for  the  -reduction  of  arsenious  acid  and  of  arsenic 
acid,  by  depriving  them  of  their  oxygen,  at  a  red  heat. 
Charcoal,  for  this  purpose,  is  employed  either  in  the  shape 
of  small  splinters,  or  reduced  to  powder.  Sometimes  the 
simultaneous  application  of  an  alkaline  carbonate  is  neces- 
sary for  the  separation  of  arsenic  ;  in  such  cases  it  is  best 
to  use  a  mixture  of  soda  in  powder  and  lamp-black ;  this 
mixture  is  heated  in  a  covered  crucible,  and  kept  in  a-  well- 
stopped  bottle. 


CARBONATE    OF    SODA.  77 

§  79. 

2.    CARBONATE  OF  SODA.       (Na  0,  CO2.) 

Preparation. — One  part  of  chrystallized  and  three  parts 
of  dried  carbonate  of  soda  are  intimately  mixed  together 
and  then  put  into  the  broken-off  neck  of  a  retort,  or  into  a 
wide  glass  tube,  or  some  vessel  of  that  description ;  one 
aperture  is  closed  by  means  of  a  perforated  cork,  the  other 
remains  open.  To  the  perforated  cork  a  tube  is  fitted, 
which  is  connected  with  a  gas  evolution  flask,  in  which, 
when  the  entire  apparatus  is  ready,  carbonic  acid  is 
evolved  from  limestone  and  hydrochloric  acid.  We  ob- 
tain in  this  manner  bicarbonate  of  soda.  The  complete 
saturation  of  the  carbonate  of  soda  with  carbonic  acid  is 
known  by  the  falling  of  the  temperature  of  the  mixture 
which  had  become  elevated  in  the  course  of  the  operation, 
and  by  the  immediate  extinction  of  an  ignited  wood-splint, 
when  held  before  the  open  aperture  of  the  tube.  The  salt 
is  then  thrown  on  a  filter-funnel  and  washed  with  cold 
water,  till  the  liquid  which  runs  off,  after  supersaturation 
with  nitric  acid,  is  no  longer  disturbed  by  chloride  of 
barium,  or  by  nitrate  of  silver;  the  salt  is  then  dried,  and 
heated  in  a  crucible  of  silver,  platinum,  or  porcelain.  Car- 
bonate of  soda  is  thus  obtained,  one  atom  of  carbonate 
acid  being  expelled.  The  purity  of  carbonate  of  soda  is 
tested  like  that  of  carbonate  of  potash.  Hydro- sulphuret 
of  ammonia  must  not  alter  its  solution. 

Uses. — We  employ  carbonate  of  soda,  on  account  of  its 
fusibility,  to  promote  the  reduction  of  oxidized  substances 
by  the  inner  flame  of  the  blow-pipe.  In  fusing  it  brings 
the  oxides  into  most  intimate  contact  with  the  charcoal  sup- 
port, and  allows  the  flame -of  the  blow-pipe  to  embrace 
every  part  of  the  specimen.  But  it  does  not  co-operate  in 
this  process  by  its  matter,  or  by  decomposition.  If  the 
quantity  operated  upon  is  very  minute,  the  reduced  metal 
will  often  be  found  in  the  pores  of  the  coal.  In  such  cases, 
the  parts  surrounding  the  little  hole  which  contained  the 
sample,  are  taken  off  with  a  knife,  triturated  in  a  mortar, 
and  the  coal  washed  off  from  the  metallic  particles,  which 
then  become  visible,  either  as  powder  or  as  small  and  flat 
spangles,  according  to  their  various  nature. 


78  CYANIDE    OP    POTASSIUM. 

In  many  cases,  e.  g.  in  the  reduction  of  peroxide  of  tin, 
it  is  advantageous  to  add  some  borax  to  the  carbonate  of 
soda,  in  order  to  render  the  mass  more  easily  fusible.     In 
the  second  place,  carbonate  of  soda  serves  as  solvent.     It 
is  best  to  use  platinum   wire  as  the  support,  when  testing 
whether  bodies  are  soluble  in  carbonate  of  soda.     For  this 
purpose  the  substance  is  made  into  a  paste  with  some  car- 
bonate of  soda  and  water ;  this  paste  is  placed  on  the  loop 
of  a  platinum  wire,  and  heated.     A  few  only  of  the  bases 
dissolve  in*  melting  carbonate  of  soda,  but  acids  dissolve 
with   facility  therein.     Silicic  acid  differs  from  all  other 
acids,  inasmuch  as  the  glass  which  it  forms  with  carbon- 
ate of  soda,  remains  clear  on  cooling,  if,  of  course,  the  two 
constituents  are  present  in   the  right  proportion  to  each 
other.     Carbonate  of  soda  is,  moreover,  applied  as  a  means 
of  decomposing,  and  rendering  other  bodies  soluble,  espe- 
cially the   insoluble  sulphates,   with  which  it  exchanges 
acids,  whilst,  at  the   same  time,  a  reduction  of  the  new- 
formed  sulphate  of  soda  to  sulphuret  of  sodium  takes  place  ; 
when  fused  together  with  sulphuret  of  arsenic,  both  are 
decomposed,  giving  rise  to  the  formation  of  sulphuret  of 
arsenic  and  sodium,  and  of  arsenite,  or  asseniate   of  soda, 
and  thus  converting  it  into  such  a  form  as  to  admit  of  its  being 
reduced  by  means  of  hydrogen.  Finally,  carbonate  of  soda 
is  the  most  susceptible  reagent  in  the  dry  way,  for  the  de- 
tection of  manganese,  since,  when  fused  together   in  the 
outer  flame  of  the  blow-pipe,  with  a  substance   containing 
manganese,  it  produces  a  green,  turbid  button,  owing  to  the 
formation  of  manganate  of  soda. 

§  80. 

3.   CYANIDE    OF    POTASSIUM.       (KCy.) 

For  the  preparation  of  this  reagent,  vide  §  40. 

Uses. — Cyanide  of  potassium  is  so  powerful  as  a  re- 
ducing agent  in  the  dry  way,  that  it  excels  in  its  action  al- 
most all  other  reagents,  and,  indeed,  it  separates  the  radi- 
cals not  only  from  oxygen  combinations,  but  also  from  sul- 
phur combinations,  giving  rise,  in  the  first  case,  to  the  for- 
mation of  cyanate  of  potash,  by  absorbing  oxygen,  and,  in 
the  latter  case,  to  the  formation  of  sulphocyanide  of  potas- 
sium. We  may,  by  means  of  this  reagent,  in  the  easiest 


CYANIDE   OF    POTASSIUM.  79 

manner  (commonly  merely  in  a  porcelain  crucible  over  a 
spirit-lamp)  obtain  pure  metals  from  their  combinations,  as 
e.  g.  antimony  from  antimonious  acid  or  from  sulphuret  of 
antimony,  iron  from  peroxide  of  iron,  &c.  &c.  The  separ- 
ation of  these  metals  is  much  promoted  by  the  easy  fusi- 
bility of  cyanide  of  potassium.  Jn  analysis,  this  reagent  is 
of  the  highest  importance,  for  the  reduction  of  arsenites 
and  arseniates,  especially  of  some  of  those  salts  which 
have  the  heavy  metals  for  bases,  and  the  reduction  of  which 
by  the  usual  means  of  deoxidizing  succeeds  only  with 
difficulty.  As  cyanide  of  potassium  is  not  yet  universally 
known  as  a  reagent  in  this  respect,  I  invite  particular  at- 
tention to  its  superior  usefulness  in  the  reduction  of  arsenic. 
For  experiments  on  a  larger  scale,  glass  tubes  are  selected, 
rounded  at  their  closed  end.  The  salt  which  it  is  intended 
to  reduce,  e.  g.  arseniate  of  silver,  is  thrown  into  a  tube  of 
this  description,  and  covered  by  a  small  piece  of  cyanide 
of  potassium  ;  all  moisture  is  first  removed  from  the  tube 
by  gently  heating  it  from  below  upwards  ;  the  cyanide  of 
potassium  is  then  heated  to  fusion  and  allowed  to  act  on 
the  test  specimen.  The  deoxidation  begins  in  a  brisk  man- 
ner, and  with  ignition  ;  it  is,  therefore,  unnecessary  to  ap- 
ply much  external  heat,  at  this  point  of  the  operation.  Up 
to  this  time,  generally,  no  incrustation  of  arsenic  appears, 
but  if  the  melting  mass  be  now  somewhat  more  strongly 
heated,  the  arsenic  will,  after  some  time,  completely  sub- 
lime ;  and  as  the  fused  mass  does  notspout,  if  the  interior 
of  the  tube  is  perfectly  dry  and  clean,  exceedingly  beauti- 
ful mirror-incrustations  will  be  obtained.  For  the  reduc- 
tion of  very  small  quantities  of  compounds  of  arsenic,  we 
use  a  perfectly  dry  mixture  of  equal  portions  of  carbonate 
of  soda  and  of  cyanide  of  potassium,  and  cover  the  test 
specimen  with  about  six  times  its  quantity  of  this  mixture  ; 
conducting  the  operation  in  a  small  glass  tube  expanded  at 
one  end  into  a  small  bulb.  From  sulphuret  of  arsenic  also 
we  may  completely  sublime  the  arsenic,  by  fusing  the 
sulphuret  together  with  cyanide  of  potassium.  Several 
arsenious  and  arsenic  metallic-salts,  when  fused  together 
with  cyanide  of  potassium,  are  reduced  in  such  a  manner 
as  .to  give  rise  to  the  formation  of  fixed  arseniuret,  (e.  g. 
arseniate  of  iron.)  In  such  cases  no  mirror  incrustations 


80  BIBORATE    OF    SODA. 

of  arsenic  are  obtained,  which  must  be  borne  in  mind. 
As  a  blow-pipe  reagent,  cyanide  of  potassium  is  also 
highly  useful  ;  its  action  is  indeed  extraordinary ;  sub- 
stances like  peroxide  of  tin,  sulphuret  of  tin,  &c.  &c., 
which  for  their  reduction  with  carbonate  of  soda,  require 
rather  a  strong  flame,  are  reduced  with  the  greatest  facility 
when  cyanide  of  potassium  is  used.  In  blow-pipe  experi- 
ments we  always  use  a  mixture  of  equal  parts  of  carbon- 
ate of  soda  and  of  cyanide  of  potassium,  since  the  cyanide 
of  potassium  alone  fuses  too  easily.  This  mixture,  be- 
sides its  more  powerful  action,  has  another  advantage  over 
carbonate  of  soda  :  it  is  with  extreme  facility  imbibed  by 
the  porous  charcoal,  so  that  the  purest  metallic  globules 
are  obtained. 

§  81. 

BIBORATE    OF    SODA.       (BORAX.)      (Na  O, '2  B,  C3.) 

The  purity  of  commercial  borax  may  be  tested,  by  add- 
ing to  its  solution,  either  carbonate  of  potash,  or,  after  a 
previous  addition  of  nitric  acid,  solution  of  nitrate  of  ba- 
rytes  or  solution  of  nitrate  of  silver.  The  borax  may  be 
considered  pure  if  these  reagents  cause  no  alteration  ;  but 
if  they  either  disturb  or  precipitate  its  solution,  it  must  be 
purified  by  recrystallization.  The  pure  crystallized  borax 
is  exposed  to  a  gentle  heat,  in  a  platinum  crucible,  till  it  no 
longer  swells  up  ;  it  is  then  triturated  and  kept  for  use. 

Uses. — Boracic  acid  shows  a  grea  affinity  for  oxides, 
when  brought  into  contact  with  them  whilst  fusing.  It 
combines,  therefore,  in  the  first  place,  directly  with  oxides. 
2.  It  expels  weaker  acids  from  their  salts  ;  and  3,  with  the 
co-operation  of  the  outer  flame  of  the  blow-pipe,  it  disposes 
metals,  sulphur  combinations,  and  haloid  combinations  to 
oxidize,  in  order  to  combine  with  the  oxides.  The  borates 
produced,  generally  fuse  readily  by  themselves,  but  by  far 
more  easily  when  fused  together  with  borate  of  soda  ;  the 
latter  salt  acts  in  this  operation  either  as  a  mere  flux,  or 
by  giving  rise  to  the  formation  of  double  salts.  In  the 
biborate  of  soda,  we  have  1,  free  boracic  acid;  and  2, 
borate  of  soda  ;  and  thus,  both  conditions  united,  by  which, 
as  before  stated,  oxides,  sulphurets,  metals,  &c.  are  dis- 


PHOSPHATE  OP  SODA  AND  AMMONIA.  81 

posed  for  solution  and  fusion  ;  borax  is,  therefore,  as  a 
blow-pipe  reagent,  of  the  greatest  importance  in  analytical 
chemistry.  We  generally  select  platinum  wire  as  support 
in  this  operation,  heating  the  loop  of  it  to  redness,  dipping 
it  into  the  borax  powder,  and  holding  it  in  the  outer  flame, 
whereby  a  colourless  pearl  is  obtained.  This  pearl  is 
brought  into  contact  with  the  test  specimen,  either  when 
still  hot,  or  after  being  moistened,  and  thus  a  small  quan- 
tity of  the  latter  attached  to  it ;  it  is  then  again  exposed, 
first,  to  the  flame  of  a  spirit-lamp,  then  to  that  of  the  blow- 
pipe, observing  the  phenomena  which  appear.  The  fol- 
lowing points  ought  to  be  examined  with  especial  care  : 
1 .  Whether  the  specimen  dissolves  transparent  or  not,  and 
whether  it  retains  this  transparency  on  cooling  or  not.  2. 
Whether  this  specimen  shows  a  distinct  and  definite  colour, 
which  in  many  cases,  e.  g.  with  cobalt,  leads  to  an  in- 
stantaneous and  certain  detection ;  and  3.  Whether  the 
pearls  show  the  same  or  a  different  relation  in  the  outer 
and  inner  flame.  Phenomena  of  the  latter  kind  depend  on 
the  mutation  from  higher  degrees  of  oxidation  to  lower,  or 
even  to  the  metallic  state,  and  are  for  some  substances  par- 
ticularly significant. 

§  82. 

5.  PHOSPHATE  OF  SODA  AND  AMMONIA.  (MICROCOSMIC  SALT.) 

(NaO,  NH4  O,  P05.) 

Preparation. — This  salt  is  obtained  by  dissolving  six 
parts  of  phosphate  of  soda  and  one  part  of  pure  sal-ammo- 
niac in  two  parts  of  hot  water,  and  allowing  the  mixture 
to  cool,  The  crystals  of  the  double  salt  thus  obtained  are 
purified  by  recrystallization  from  the  chloride  of  sodium 
which  still  adheres  to  them.  They  are  then  dried,  pow- 
dered, and  kept  for  use. 

Uses.  —  When  phosphate  of  soda  and  ammonia  is  heat- 
ed, the  ammonia  escapes  together  with  the  water  of  crys- 
tallization. There  remains,  consequently,  a  compound, 
which,  with  regard  to  composition,  (free  acid  and  fusible 
salt,)  very  nearly  approaches  borax.  The  action  of  mi- 
crocosmic  salt  is,  therefore,  quite  analogous  to  that  of 
biborate  of  soda.  We  prefer  it,  however,  to  borax  in  many 
cases  as  a  solvent  or  flux,  knowing,  by  experience,  that  the 


82  PROTO-NITRATE    OF   COBALT. 

glasses  which  it  forms  with  many  substances,  are  more 
beautifully  and  distinctly  coloured  than  those  of  borax. 
Platinum  wire  is  equally  used  as  a  support  when  employ- 
ing microcosmic  salt  as  a  flux ;  it  ought,  however,  here  to 
be  remarked,  that  the  loop  of  the  wire  must  be  small  and 
narrow,  or  else  the  pearl  will  not  stick  to  it.  The  opera- 
tion is  conducted  as  stated  §  81  in  the  preceding  paragraph. 

§  83. 

PROTO-NITRATE    OF    COBALT.       (CoO,  NO5.) 

Preparation. — To  obtain  this  reagent,  an  intimate  mix- 
ture of  two  parts  of  very  finely  pounded  cobalt,  four  parts 
of  saltpetre,  one  part  of  effloresced  carbonate  of  soda,  and 
one  part  of  dry  carbonate  of  ipotash,  is  projected  in  small 
portions  in^o  a  crucible  heated  to  redness  ;  the  latter  is 
then  left  exposed  to  the  strongest  possible  heat,  till  the 
mass,  although  perhaps  not  in  perfect  fusion,  yet  is  melt- 
ing. The  mass  is  then  allowed  to  cool,  and  afterwards 
reduced  to  powder  and  boiled  with  water ;  the  impure 
peroxide  of  cobalt  obtained  is  completely  washed,  digested 
and  heated  with  hydrochloric  acid  until  dissolved.  This 
solution  is  of  a  dark  green  colour,  and  generally  ge- 
latinous, owing  to  the  separation  of  silicic  acid.  It  is 
evaporated  to  dryness,  the  residue  boilefl  with  water,  fil- 
tered, and  carbonate  of  ammonia  added  to  the  filtrate, 
whilst  kept  at  the  boiling  point,  till  all  acid  reaction  ceases. 
The  filtered  solution  is  precipitated  by  means  of  carbonate 
of  potash,  the  precipitate  obtained  washed,  and  then  dis- 
solved in  nitric  acid.  The  solution  is  evaporated  to  dry- 
ness,  at  a  gentle  heat,  and  one  part  of  the  residue  dissolved 
in  ten  parts  of  water,  for  use. 

Uses. — The  protoxide  of  cobalt,  when  heated  with  cer- 
tain infusible  substances,  forms  with  them  combinations  of 
divers  various  characteristic  colours,  and  may,  therefore, 
serve  for  the  detection  of  those  substances.  Experiments 
of  this  kind  are  conducted  in  the  following  manner.  The 
substance  under  examination,  reduced  to  powder,  is  heated 
to  redness,  on  a  charcoal  support,  the  smallest  possible  drop 
of  solution  of  proto-nitrate  of  cobalt  is  then  dropped  upon 
it,  and  it  is  again  heated  to  redness.  In  this  process, 


RELATION    OF    SUBSTANCES    TO    REAGENTS.  83 

oxide  of  zinc  assumes  an  intensely  green  colour,  alumina 
a  blue,  and  magnesia  a  feeble  rose  tint.  The  rose  tint  of 
magnesia  is  of  so  little  intensity  that  beginners  may  easily 
overlook  this  reaction.  Silica  also,  when  moistened  with 
solution  of  nitrate  of  cobalt  and  heated  to  redness,  assumes 
a  feeble  blue  tint,  which  ought  to  be  borne  in  mind  when 
testing  for  alumina.  The  blue  compound  of  the  latter  is, 
however,  by  far  more  beautifully  and  intensely  coloured, 
than  that  of  silica. 


CHAPTER  III. 

ON  THE  RELATION  OF  THE  VARIOUS  SUBSTANCES  TO 
REAGENTS. 

§  84. 

As  we  have  stated  in  our  introductory  remarks,  qualita- 
tive analysis  is  based  on  experiments  by  means  of  which 
we  endeavour  to  convert  the  unknown  constituents  of  a 
substance  into  forms  with  the  relations  and  properties  of 
which  we  are  familiar,  so  as  to  enable  us  to  determine  the 
nature  of  constituents.  It  is  the  same  with  such  experi- 
ments as  with  inquiries  and  investigations  in  general.  They 
are  the  better  the  more  certainly  they  lead  to  a  definite  re- 
sult, no  matter  whether  of  a  positive  or  negative  charac- 
ter. But  as  a  question  does  not  render  us  a  whit  the  wiser, 
if  we  do  not  understand  the  language  in  which  the  answer 
is  returned,  so  an  experiment  cannot  avail  us  if  we  do 
not  know  the  manner  of  expression  in  which  the  infor- 
mation is  conveyed  to  us,  i.  e*,  if  we  do  not  know  what 
conclusion  we  are  to  draw  from  a  reagent  leaving  a  body 
unaltered,  or  producing  some  phenomenon  or  other, 
owing  to  a  mutation  of  form,  or  state,  in  the  substance 
operated  upon. 

Before  we  can,  therefore,  proceed  to  the  practice  of 
analysis,  we  must,  as  an  indispensable  condition,  first  really 
and  completely  know  those  forms  and  combinations  of  sub- 
stances, which  are  supposed  to  be  known.  But  this  perfect 
knowledge  depends  first,  on  a  comprehensive  conception  of 


84  POTASH,  SODA,  AMMONIA. 

the  conditions  which  are  necessary  for  the  formation  of  the 
new  combinations,  and  thus,  in  short,  for  the  mani- 
festation of  the  various  reactions  ;  and  2dly,  on  a  dis- 
tinct impression  of  the  colour,  form,  and  physical  pro- 
perties in  general  which  characterize  the  new  combina- 
tions. 

It  is,  therefore,  of  paramount  importance  to  the  student, 
not  merely  theoretically  to  study  this  branch  of  qualitative 
analysis,  but  also,  by  actual  experiments,  to  verify  every 
part  of  it.  To  teach  the  relation  of  the  various  bodies  to 
reagents,  it  is  usual,  in  works  like  the  present,  to  treat  of 
the  substances  individually  and  separately,  and  to  point 
out  their  characteristic  reactions.  I  have,  however,  in  the 
present  work,  deemed  it  more  judicious  and  better  adapted 
to  its  elementary  character,  to  collect  into  groups  those 
substances  which  are  in  many  respects  analogous,  and 
thus,  by  confronting  their  analogies  with  their  differences, 
to  'place  the  latter  in  the  clearest  possible  light. 

A. RELATION    OF    THE    METALLIC  OXIDES. 

§  85. 
First  Group. 

POTASH,    SODA,     AMMONIA. 

Properties  of  the  Group.  — The  alkalies  are  easily  solu- 
ble in  water,  as  whether  in  their  pure — or  caustic  state — 
or  as  sulphurets  and  carbonates.  They,  therefore,  do  not 
precipitate  each  other,  neither  in  their  pure  state  nor  as 
carbonates,  nor  are  they  precipitated  by  sulphuretted  hy- 
drogen under  any  condition  whatever.  The  solutions  of 
the  purer  alkalies,  as  well  as  of  their  sulphurets  and  car- 
bonates, tinge  reddened  litmus  paper  blue,  and  impart  an 
intensely  brown  tint  to  turmeric  paper* 

Special  reactions  characteristic  of  the  individual   sub- 
stances, 

a.  POTASH.     (K  O.) 
1.  The  salts  of  potash  are  not  volatile  in  the  heat  of  a 


POTASH,    SODA,  AMMONIA.  85 

spirit-lamp.  They  almost  all  dissolve  in  water  with  facility. 
Their  solutions  are  colourless  provided  the  constituent  acid 
be  so.  The  neutral  salts  of  potash  with  strong  acids,  do 
not  affect  vegetable  colours.  Carbonate  of  potash  is  of 
difficult  crystallization.  The  dry  salt  as  well  as  the  crys- 
tals, (KO,  COa,  2aq.)  which  are  formed  in  concentrated 
aqueous  solutions  of  carbonate  of  potash,  when  allowed  to 
stand  for  some  time,  deliquesce  with  rapidity  when  exposed 
to  humid  air. 

2.  Chloride  of  platinum  produces  in  the  neutral  and  acid 
solutions  of  the  salts  of  potash,  a  yellow  crystalline  heavy 
precipitate.     (CHLORIDE  OF  PLATINUM  AND  POTASSIUM.  K 
C1+  P-f-  C12.)     In  concentrated  solutions,  the  formations 
of  this  precipitate  is  immediate,  in  dilute  solutions  it  takes 
place    after    a    short   time,    and   frequently    even    after 
the  lapse  of  some  time.     The  presence  of  free  hydrochloric 
acid   promotes  its  formation.      It  is  difficultly  soluble   in 
water,  and  wholly  insoluble  in  alcohol.     Chloride  of  plati- 
num is,  therefore,  a  particularly  delicate  test  for  salts  of 
potash  when  the  latter  is  in  alcoholic  solution.    Care  should 
be  taken  to  avoid  confounding  chloride  of  platinum  and 
potassium  with  chloride  of  platinum  and  ammonium. 

3.  Tartaricacid  produces,  in  neutral  or  alkaline  solutions 
of  salts  of  potash,  (to  alkaline  solutions  the  reagent  must 
be  added  till  a  strongly  acid  reaction  becomes  manifest,)  a 
white,  quickly  subsiding,  granular  crystalline  precipitate 
of  BI-TARTRATE  OF  POTASH.  (KO,  HO,  T.)     In  concen- 
trated  solutions  this  precipitate  is  formed  immediately,  in 
dilute  solutions  frequently  only  after  the  lapse  of  some  time. 
Violent  agitation  of  the  liquid  considerably  promotes  the  for- 
mation of  the  precipitate.    Free  alkalies  and  free  mineral 
acids  dissolve  the  precipitate  ;  it  is  difficultly  soluble  in 
cold,  but  more  easily  so  in  hot  water. 

4.  When  salts  of  potash,  by  means  of  a  platinum  wire, 
are  held  in  the  summit  of  the  inner  blow-pipe  flame,  the 
outer  flame  assumes  a  VIOLET  tint,  owing  to  a  reduction  of 
potash,  and  a  reoxidation  of  the  potassium  thus  formed.  This 
reaction  is  hardly  perceptible  in  phosphates  and  borates  of 
potash.     The  presence  of  soda  renders  it  completely  im- 
perceptible. 

5.  When  a  salt  of  potash  is  heated  with  a  small  quantity 

4 


86 

of  water,  alcohol  added,  and  the  latter  ignited,  the  flame 
appears  VIOLET.  The  presence  of  soda  renders  this  reac- 
tion also  imperceptible. 

b.  SOI>A.  (Na  O.) 

1 .  The  salts  of  soda  present  the  same  general  relations 
as  those  of  potash.     Carbonate  of  soda  crystallizes  readily ; 
the  crystals  (Na  O,  CO2  +  10  aq.)  effloresce  rapidly  when 
exposed  to  dry  air. 

2.  If  a  neutral  or  alkaline  solution  of  a  soda  salt  be  mix- 
ed with  a  solution  of  neutral  antimoniate  of  potash*   a 
white  granular  crystalline    precipitate,,  ANTIMONIATE   OP 
SODA  (Na  O,  Sb  O  6 )  is  formed,  (in  concentrated  solutions, 
almost  immediately,  in  dilute  solutions  after  the  lapse  of 
some  time.)     Violent  agitation  of  the  mixture  promotes  the 
separation  of  the  precipitate  very  much ;  rubbing  the  inner 
sides  of  the  vessel  with  a  glass  rod  is  even  more  effective. 
Even  in  solutions  of  soda,  diluted  to  the  extent  of  1000  to 
1,  we  observe,  after  the  lapse  of  some  time,  a  certain  milk- 
iness,  and,  finally,  the  formation  of  a  crystalline  precipitate. 
This  reaction  is  not  interfered  with  by  the  presence  of  salts 
of  potash  ;  the  presence  of  carbonate  of  potash,  in  excess, 
alone  has  a  preventive  influence  on  the  formation  of  the 
precipitate,  since  antimoniate  of  soda  dissolves  more  readily 
in  solution  of  carbonate  of  potash,  than  in  water.     The 
presence  of  free  acids  must  always  be  avoided,  since  they 
separate  from  the  reagent,  bi-antimoniate  of  potash,  or  hy- 
drate of  antimonic  acid,  in  the  form  of  a  white  precipitate. 

3.  Salts  of  soda  exposed  on  a  platinum  wire  to  the  inner 
blow-pipe  flame,   colour  the  outer  flame  INTENSELY  YEL- 
LOW, owing  to  a  reduction  of  soda,  and  a  re-oxidation  of 
the   sodium  formed.     This  reaction  is  visible   even  if  a 
large  quantity  of  potash  is  mixed  with  the  soda. 

*  This  reagent  is  prepared  by  exposing  fifty  parts  of  antimoniuro 
diaphoreticum  ablutum,  mixed  with  twenty  and  four  tenth  parts  of  pure 
carbonate  of  potash,  to  a  red  heat  for  half  an  hour.  The  crumbling 
mass  is  kept  in  a  well-stopped  glass  vessel.  The  solution  is  prepared 
by  drenching  four  parts  of  the  powder  with  one  hundred  parts  of 
warm  water,  allowing  it  to  digest,  and  to  cool  completely,  and  then 
filtering  the  solution  and  preserving  the  clear  filtrate,  protected  from 
the  access  of  air. 


AMMONIA.  87 

4.  When  a  salt  of  soda  is  heated  with  a  small  quantity 
of  water,  alcohol  added,  and  the  latter  ignited,  the  flame 
appears  strongly  YELLOW.     The  presence  of  a  salt  of 
potash  has  no  preventive  influence  on  this  reaction* 

5.  Chloride  of  platinum  produces  no  precipitate,  in  so- 
lutions of  soda :  tartaric  acid  only  when  they  are  highly 
concentrated.     The  BITARTATE  OF  SODA,  (Na  O,  HO,  T  + 
2  aq.)  which  crystallizes  out  in  such  cases,  appears  always 
in  the  shape  of  small  needles  and  columns,  and  not,  like 
the  corresponding  salt  of  potash,  in  the  form  of  a  granular 
crystalline  precipitate.  . 

C.   AMMONIA.   (NH4  O.)  /] 

\ .  All  salts  of  ammonia  are  volatile  at  a  high  lempera- 
ture,  either  with  decomposition,  or  remainingin  combina- 
tion. Most  of  them  are  easily  soluble  in  water.  Their 
solutions  are  colourless.  The  neutraF  ammoniacal  com- 
pounds with  strong  acids  do  not  alter  vegetable  colours. 

2.  When  salts  of  ammonia  are  triturated  with  hydrate 
of  lime,  with  the  addition  of  a  few  drops  of  water,  or  when 
they  are  heated,  either  in  a  solid  forrri  or  in  solution,  with 
solution  of  potash,  ammonia  becomes  liberated  in  its 
gaseous  state,  and  manifests  itself,  1 ,  by  its  characteristic 
odour  ;  2,  by  its  reaction  on  moistened  test-papers ;  and 
3,  by  giving  rise  to  the  formation  of  white  fumes,  when 
any  object  (e.  g.  a  glass  rod)  moistened  with  hydrochloric 
acid,  nitric  acid,  acetic  acid,  any  volatile  acids,  is  brought 
in  contact  with  it.  These  fumes  are  caused  by  the  forma- 
tion of  fixed  salts,  produced  by  the  contact  of  the  gases  in 
the  air.  Hydrochloric  acid  is  the  most  delicate  test  in  this 
experiment;  acetic  acid,  however,  less  easily  admits  of 
any  mistake. 

3.  Chloride  of  platinum  shows  the  same  relation  to  salts 
of  ammonia  as  to  salts  of  potash  ;  the  yellow  precipitate 

of  CHLORIDE  OF  PLATINUM  AND  AMMONIUM  (NH4   C14-P  + 

C12)  has,  however,  a  somewhat  lighter  colour  than  chloride 
of  platinum  and  potassium. 

c-  Tartaric  acid  produces  in  solutions  of  salts  of  ammo- 
nia a  precipitate  of  BITARTRATE  OF  AMMONIA,  (NH4  O, 
HO,  T,)  which  is  formed  in  the  same  manner,  and  under 
the  same  circumstances  as  the  corresponding  salt  of  potash, 
but  is  somewhat  more  soluble  than  the  latter. 


88  BARYTES,    STRONTIAN,    LIME,    MAGNESIA. 

Recapitulation  and  remarks. — Salts  of  potash  and  of 
soda  are  not  volatile  at  a  conjmon  red  heat ',  salts  of 
ammonia  volatilize  easily.  The  latter  may,  therefore,  be 
easily  separated  from  the  former  by  the  application  of  a 
red  heat.  The  surest  test  of  ammonia  is  its  expulsion  by 
lime  or  potash.  Salts  of  potash  can  only  be  detected 
when  salts  of  ammonia  are  removed,  since  both  show  the 
same  or  similar  relations  to  chloride  of  platinum  and  tar- 
taric  acid.  Potash  is  characterized  with  certainty  by 
either  of  these  two  reagents,  when  ammonia  is  removed. 
Soda  can  only  be  positively  detected  by  the  figure  of  crys- 
tallization, and  the  properties  of  some  of  its  salts  by  its  be- 
haviour with  antimoniate  of  potash,  and  by  the  colour  which 
its  salts  impart  to  the  flame  of  the  blow-pipe,  and  to  that  of 
alcohol.  When  testing  for  soda  with  antimoniate  of  pot- 
ash, ammoniacal  salts  must  not  be  present,  as  they  also 
yield  precipitates  with  the  same  reagent.  If  the  soda  is 
combined  with  potash  in  alkaline  solution,  and  we  intend 
to  test  for  it  with  antimoniate  of  potash,  acetic  acid,  or 
hydrochloric  acid,  must  first  be  added,  until  the  alkaline 
reaction  has  nearly  but  yet  not  completely  disappeared. 
If  the  fluid  under  examination  contains  a  free  acid,  pure 
carbonate  of  potash  is  added,  until  the  solution  has  acquired 
an  incipient  alkaline  reaction. 

§  86.  .  A 

Second  Group. 

BARYTES,    STRONTIAN,    LIME,    MAGNESIA. 

Properties  of  the  group. — The  alkaline  earths  are  solu- 
ble in  water,  in  their  caustic  state  and  as  sulphurets. 
Magnesia,  however,  is  very  difficult  of  solution.  These 
solutions  manifest  alkaline  reactions.  The  neutral  carbo- 
nates and  phosphates  of  the  alkaline  earths  are  insoluble 
in  water.  The  solutions  of  the  salts  of  the  alkaline  earths 
are,  therefore,  not  precipitated  by  sulphuretted  hydrogen, 
under  any  condition,  but  alkaline  carbonates  and  phos- 
phates do  precipitate  them.  This  relation  distinguishes 
the  oxides  of  the  second  group  from  those  of  the  first. 
The  salts  of  the  alkaline  earths  are  colourless,  partly 
soluble,  partly  insoluble,  and  not  volatile. 


BARYTES.  89 

Special  Reactions-.  ") 

a.  BARYTES.  (Ba  O.) 

1.  Ammonia  causes  no  precipitate  in  the  solutions  of 
salts  of  barytes  ;  POTASH  only  when  they  are  concentrated. 
Water  re-dissolves  the  precipitate  of  HYDRATE  OF  BARYTES 
(Ba  O-f-aq.)  which  is  formed. 

2.  Alkaline  carbonates  throw  down  from  solutions  of 
barytes   CARBONATE  OF  BARYTES,  (Ba  O,  CO2.)  in  the 
form  of  a  white  precipitate.     In  acid  solutions,  however, 
complete  precipitation  takes  place  only  on  boiling ;  the 
same  is  the  case  when  carbonate  of  ammonia  is  employed 
as   the   precipitant.     The  presence  of  salts  of  ammonia 
does  not  prevent  this  precipitation. 

3.  Sulphuric  acid,  and  all  the  soluble  sulphates,  pro- 
duce, even  in  the  most  highly  diluted  solutions  of  barytes, 
immediately,    a  fine    white    precipitate,     SULPHATE     OF 
BARYTES,  (Ba  O,  SO3J)  which  is  insoluble  in  acids  and 
alkalies. 

4.  Hydrofluo-silicic  acid  precipitates  from  solution  of 
barytes  SILICOFLUORIDE  OF  BARIUM,  (3  Ba  Fl-J-2  Si  F13,) 
in  the  form  of  a  colourless,  crystalline,  quickly-subduing 
precipitate.     In  dilute  solutions  this  precipitate  is  formed 
only  after  the  lapse  of  some  time ;  hydrochloric  acid  and 
nitric  acid  dissolve  it,  but  only  to  a  hardly  perceptible 
extent. 

5.  Phosphate  of  soda  causes  in  neutral  or  alkaline  solu- 
tion,   a  white    precipitate  of   PHOSPHATES    OF  BARYTES, 
(Ba  O,  PO5)  which  is  soluble  in  free  acids.     Addition  of 
ammonia  neither  increases  the  quantity  of  this  precipitate, 
nor  promotes  its  formation. 

6.  Oxalic  acid  causes  only  in  concentrated  solutions  a 
white  precipitate  of  OXA.LATE  OF  BARYTES,  (Ba  O,  O-Htq.) 
which  is  soluble  in  acids.     But  if  ammonia  be  added,  the 
reaction  is  by  far  more  susceptible,  anS  the  solution  must 
be  highly  dilute  indeed  if  no  precipitate  is  formed. 

7.  Salts  of  barytes,  when  heated  with  diluted  spirit 
of  wine,  impart  to  the  flame  of  the  latter  a  but  little  cha- 
racteristic YELLOWISH  Colour. 


90  STRONTIAN.       LIME. 

b.    STRONTIAN.    (Sr  O.) 

1.  Salts  of  strontian  show   completely  the  same  rela- 
tions as  salts  of  barytes,  to  ammonia  and  potash,  as  well 
as  to  the  alkaline  carbonates  and  to  phosphate  of  soda. 

2.  Sulphuric  acid  and  sulphates  precipitate  from  solu- 
tions of  strontian,  SULPHATE   OF   STRONTIAN,  (Si  O,  SO3,) 
in  form  of  a  while  powder,  which  is  insoluble  in  acids  and 
alkalies.     Sulphate  of  strontian  is  by  far  more  soluble  in 
water  than  sulphate  of  barytes,  owing  to  whith  the  preci- 
pitate in  rather  dilute  solutions  is  generally  only  formed 
after  the  lapse  of  some  time  ;  and  this  is  always  the  case 
(even  in  concentrated  solutions)  if  solution  of  gypsum  is 
employed  as  the  precipitant. 

3.  Hydrofluo-silicic  acid  does  not  cause  any  precipi- 
tate, even  in  concentrated  solutions  of  strontian. 

4.  Oxalic  acid  precipitates   even  from  rather  highly 
dilute  solutions,  after^the  lapse  of  some  time,  OXALATE  OF 
STRONTIAN,  (Sr  O,  O-faq.)  as  a  white  powder.     Addition 
of  ammonia  promotes  the  formation  of  the  precipitate,  and 
considerably  increases  its  quantity. 

5.  If  such  salts  of  strontian  as  are  soluble  in  water  or 
alcohol,   be  heated  with  diluted   alcohol,  and  the   latter 
ignited,  they  impart  to  its  flame,  especially  on  stirring,  an 
intense  CARMINE  RED  colour.     This  colour  must  not  be 
confounded  with  that  which  salts  of  lime  communicate  to 
the  flame  of  alcohol. 

c.  LIME.  (Ca  O.) 

1.  Ammonia,  potash,  alkaline^arbonates,  and  phosphate 
of  soda,  show  the  same  relations  to  salts  of  lime  as  to  sails 
of  barytes. 

2.  Sulphuric  acid  and  sulphate  of  soda  produce  in  high- 
ly-concentrated solutions  of  lime  immediately,  white  pre- 
cipitates of  SULP^TE  OF  LIME,  (Ca  O,  SO3,  HO-f-aq.) 

I  which  are  completely  dissolved  by  a  large  proportion  of 
!  water,  but  are  far  more  soluble  in  acids  than  in  water.  In 
less  concentrated  solutions  the  precipitates  are  only  formed 
after  the  lapse  of  some  time  ;  and  no  precipitation  what- 
ever takes  place  in  highly  dilute  solutions.  Solution  of 
gypsum,  of  course,  cannot  produce  any  precipitate  ;  but 


MAGNESIA.  91 

even  a  cold  saturated  solution  of  sulphate  of  potash,  mixed 
with  an  equal  quantity  of  water,  produces  no  precipitate 
in  solutions  of  lime,  at  least  never  immediately.  If  solu- 
tions of  lime  are  so  highly  dilute,  that  sulphuric  acid  causes 
mo  precipitation  in  them,  a  precipitate  is  immediately 
formed  on  the  addition  of  alcohol. 

3.  Hydrofluo-silicic  acid  does  not  precipitate  salts  of 
lime. 

4.  Oxalic  acid  produces  a  white  precipitate  of  ox  A  LATE 
OP  LIME,  (Ca  O,  O  +  2  aq.)  even  in  highly  dilute  neutral 
solutions  of  lime.     Addition  of  ammonia  promotes  the  for- 
mation of  this  precipitate,  and  increases  its  quantity.  Oxa- 
late  of  lime  is  easily  soluble  in  hydrochloric  acid  and  nitric 
acid,  but  not  in  acetic  acid,  nor  in  oxalic  acid. 

Soluble  salts  of  lime,  when  heated  with  dilute  alcohol, 
impart  to  the  flarne  of  the  latter  a  YELLOWISH  RED  colour, 
which  is  often  confounded  with  that  caused  by  strontian. 

d.    MAGNESIA.    (Mg  O.) 

1 .  Ammonia  throws  down  from  the  solutions  of  neutral 
salts  of  magnesia,  a  portion  of  the  magnesia  as  HYDRATE 
OF  MAGNE-SIA,  (Mg  O,  HO,)  in  the  form  of  a  white  bulky 
precipitate.     The  other  portion  of  magnesia  remains  in  so- 
lution, combined  with  the  salt  of  ammonia  to  which  the 
decomposition  has  given  rise,  and  forming  with  it  a  double 
salt,  not  decoinposible  by  ammonia.     This  disposition  of 
the  salts  of  magnesia  to  form  such  double  salts  with  salts 
of  ammonia,  is  the  cause  that  salts  of  magnesia  are  not  pre- 
cipitated when  salts  of  ammonia  are  present,  or,  what  is  in 
fact  the  same,  that  ammonia  does  not  produce  any  preci- 
pitate in  acid  solutions  of  magnesia,  and  that  a  precipitate 
caused  by  ammonia,  in  neutral  solutions,  is  re-dissolved  on 
the  addition  of  a  salt  of  ammonia. 

2.  Potash  and  caustic  barytes  precipitate  from  solutions 
of  magnesia,  HYDRATE  OF   MAGNESIA.     The  formation  of 
this  precipitate  is  much  promoted  by  boiling.     Salts  of  am- 
monia redissolve  the  precipitated  hydrate  ;  and  no  precipi- 
tate is  formed  at  all,  if  they  are  mixed  in  sufficient  quantity 
with  the  magnesia  solution,  before  the  addition  of  the  pre- 
cipitant.    But  it  will,  of  course,  make  its  appearance  if  the 


92  MAGNESIA. 

solution  be  then  boiled  with  an  excess  of  potash,  for  in 
that  case  the  condition  of  its  remaining  in  solution,  i.  e.  the 
salt  of  ammonia,  becomes  decomposed  and  is  thus  re- 
moved. 

3.  Carbonate  of  potash  causes  in  neutral  solutions  of 
magnesia  a  white  precipitate,  A  COMPOUND  OF  ONE  EQUIV- 
ALENT    OF  HYDRATE     OF    MAGNESIA,    AND    THREE  EQUIVA- 
LENTS   OF     CARBONATE    OF     MAGNESIA.       (Mg    O,   HO  +  3 

Mg  O,  CO2.)  The  fourth  part  of  the  carbonic  acid  con- 
tained in  the  carbonate  of  potash  becomes  liberated  on  the 
decomposition  of  this  salt,  and  combining  with  a  portion  of 
the  new-formed  carbonate  of  magnesia,  keeps  this  part  in 
solution  as  a  bicarbonate  of  magnesia.  This  carbonic 
acid  may  be  expelled  by  boiling  ;  the  application  of  heat  to 
the  solution,  therefore,  promotes  the  formation  and  in- 
creases the  quantity  of  the  precipitate.  Salts  of  ammonia 
prevent  this  precipitation  also,  and  re-dissolve  a  precipitate 
already  formed. 

4.  Carbonate  of  ammonia  does  not  precipitate  solutions 
of  magnesia  when  cold,  and  but  imperfectly  when  boiling. 
The  addition  of  salts  of  ammonia  completely  prevents  the 
formation  of  a  precipitate. 

Phosphate  of  soda  precipitates  PHOSPHATE  OF  MAGNE- 
SIA (2  Mg  O,  PO5)  as  a  white  powder,  from  solutions  of 
magnesia,  provided  they  be  not  too  highly  dilute.  The 
precipitation  is  much  promoted  by  boiling  the  solution. 
But  if  ammonia  be  added  to  even  a  highly  diluted  solution 
of  magnesia,  no  matter  whether  before  or  after  the  addi- 
tion of  the  phosphate  of  soda,  a  white  crystalline  precipi- 
tate Of  BASIC  PHOSPHATE  OF  MAGNESIA  AND  AMMONIA 

(2  Mg  0,  NH4  O,)  (POS  +  2  HO  +  10  aq.)  is  formed. 
Its  separation  from  dilute  solutions  is  much  promoted  by 
violent  stirring  (with  a  glass  rod,)  if  even  the  solution  is  too 
highly  diluted  as  to  admit  of  the  formation  of  a  precipitate ; 
yet,  white  lines  appear  after  some  time  in  those  places  of 
the  sides  of  the  vessel  which  have  been  touched  by  the 
glass  rod  whilst  stirring  the  fluid.  Muriate  of  ammonia 
and  salts  of  ammonia,  in  general,  do  not  dissolve  the  basic 
phosphate  of  magnesia  and  ammonia,  but  it  is  soluble  in 
free  acids,  (even  in  acetic  acid.) 

6.   Oxalate  of  ammonia  (but  not  free  oxalic  acid)  pro- 


MAGNESIA.  93 

duces  a  white  precipitate  of  OXALATE  OF  MAGNESIA.  (Mg 
O,  0  -f-  2  aq.)     Salts  of  ammonia  prevent  its  formation. 

7.  Sulphuric  acid  and  hydrofluo-silicic  acid  do  not  pre- 
cipitate salts  of  magnesia. 

8.  If  magnesia,  or  a  salt  of  magnesia,  be  moistened  with 
solution  of  protonitrate  of  cobalt,  and  for  some  time  ex- 
posed on  a  coal  to   a  strong  blow-pipe  flame,  a  FEEBLY 
FLESH-COLOURED  mass  is  obtained,  the  tint  of  which  only 
becomes  distinct  on  cooling,  but  is  never  very  intense. 

Recapitulation  and  remarks.  — The  difficult  solubility 
of  the  hydrate  of  magnesia,  the  easy  solubility  of  the 
sulphate  of  magnesia,  and  the  disposition  of  salts  of  mag- 
nesia to  form  double  salts  with  salts  of  ammonia,  are 
the  three  main  points  in  which  magnesia  differs  from  the 
other  alkaline  earths.  To  detect  magnesia,  we  remove 
always  first barytes,  strontian,  and  lime,  if  they  are  present; 
and  we  effect  this  purpose,  either  by  boiling  with  carbon- 
ate of  ammonia  with  addition  of  sal  ammoniac,  or  by 
means  of  sulphate  of  potash  and  of  oxalate  of  ammonia, 
with  addition"  of  sal  ammoniac,  and  then  select  for  the  de- 
tection of  magnesia,  the  reaction  with  phosphate  of  soda, 
with  addition  of  ammonia.  The  detection  of  barytes  is  al- 
ways easy,  for  the  immediately  forming  precipitate  which 
it  yields  with  solution  of  gypsum,  and  its  reaction  with 
hydrofluo  silicic  acid,  leave  no  doubt  as  to  its  presence. 
Strontian  may  also  easily  be  detected  by  its  relation  to  so- 
lution of  gypsum,  except  in  cases  where  barytes  is  present. 
It  must,  therefore,  in  such  cases  first  be  separated  from 
barytes.  This  separation  may  best  be  effected  by  con- 
verting both  earths  into  dry  chlorides,  and  digesting  the 
latter  with  absolute  alcohol.  The  chloride  of  strontian  dis- 
solves whilst  the  chloride  of  barium  remains  undissolved. 
When  testing  for  strontian  by  means  of  the  alcohol  flame, 
we  must  avoid  confounding  the  colour  it  imparts  to  it,  with 
that  communicated  by  salts  of  lime.  For  the  detection  of 
lime,  oxalic  acid  is  always  selected.  Barytes  and  strontian 
must,  however,  first  have  been  removed  by  means  of  sul- 
phate of  potash,  since  they  manifest  with  oxalic  acid  an 
analogous  reaction,  only  varying  in  intensity.  On  the 
separation  of  barytes  and  strontian,  by  means  of  sulphate 
4* 


94  ALUMINA,    OXIDE    OF   CHROMIUM. 

ot  potash,  it  may  possibly  happen  that  also  a  portion  of  the 
lime  precipitates.  This  is,  however,  a  matter  of  indiffer- 
ence, since,  at  any  rate,  sufficient  remains  dissolved  in  the 
fluid  to  admit  of  its  presence  being  ascertained  with  in- 
dubitable certainty,  by  means  of  oxalic  acid. 

§87. 
Third  Group. 

ALLUMINA,  OXIDE  OF  CHROMIUM. 

Properties  of  the  group. — Alumina  and  oxide  of  chro- 
mium are  both  in  their  pure  state,  and,  as  hydrates,  inso- 
luble in  water.  They  form  no  neutral  salts  with  carbonic 
acid.  Their  sulphur  combinations  cannot  be  formed  in 
the  humid  way.  Sulphuretted  hydrogen,  therefore,  does 
not  precipitate  solutions  of  alumina  or  oxide  of  chromium ; 
hydrosulphuret  of  ammonia  precipitates  the  hydrated 
oxides  from  these  solutions.  This  relation  to  hydrosul- 
phuret of  ammonia  distinguishes  the  oxides  "of  the  third 
from  those  of  the  two  preceding  groups. 

Special  Reactions, 
a.  ALUMINA.  A12  O3.) 

1.  The  salts  of  alluminaare  colourless,  for  the  most  part 
not  volatile ;  some  of  them  are  soluble,  others  insoluble. 
The  soluble  salts  redden  litmus  paper  and  lose  their  acids 
when  heated  to  redness. 

2.  Potash  throws  down  from  the  solutions  of  alumina  a 
bulky  precipitate  of  HYDRATE  OF  ALUMINA,  (Ala  O  3  +HO,) 
containing  potash,  which  easily  and  completely  dissolves 
in  an  excess  of  the  precipitant,  but  may  again  be  preci- 
pitated from  this  solution  by  the  addition  of  hydrochlorate 
of  ammonia,  even  when  the  solution  is  cold,  but  more  com- 

.  pletely  on  heating  it.     The  presence  of  salts  of  ammonia 
does  not  prevent  this  precipitation  by  potash. 

3.  Ammonia  also   produces  a  precipitate  of  HYDRATE 
OF  ALUMINA  ;  and  this  precipitate  also  is  redissolved  by  a 
very  considerable   excess   of  the  precipitate,  but  only  in 
such  cases  where  the  solution  of  alumina  contains  no  salts 
of  potash  or  soda.     But  if  a  certain  quantity  of  these  salts 
is  present,  ammonia  is  not  able  to  redissolve  the  precipi- 

\  tate  first  formed. 


OXIDE   OF    CHROMIUM.  35 

Upon  this  relation,  the  complete  precipitation  of  the 
hydrate  of  alumina  from  a  potash  solution,  by  means  of 
hydrochlorate  of  ammonia,  depends.  For  in  this  process, 
potash  and  hydrochlorate  of  ammonia  mutually  decompose, 
giving  rise  to  the  formation  of  chloride  of  potassium  and 
of  ammonia  ;  and  ammonia  not  being  able  to  maintain  the 
hydrate  of  alumina  in  solution,  when  a  salt  of  potash  is 
present,  this  hydrate  of  course  precipitates, 

4.  If  alumina,  or  a  compound  of  alumina,  be  heated  to 
redness,  on  charcoal,  before  the  blow-pipe,  and  then  mois- 
tened with  a  few  drops  of  solution  of  protonitrate  of  cobalt, 
and  again  strongly  heated,  an  unfused  mass  of  a  deep  SKY- 
BLUE  colour  is   obtained,  a  compound  of  the  s 
The  colour  becomes  distinct  only  on  cooling* 
light  it  appears  violet. 

&,     OXIDE    OF    CHROMIUM.       (Cl2    O3.) 

1.  The  solutions  of  the  compounds  of  oxide  of  chro- 
mium, have  always,  even  when  highly  diluted,  either  an 
emerald-green  or  a  nigrescent  violet  colour.     The  soluble 
neutral  salts  of  oxide  of  chromium  redden  litmus  paper, 
and  are  decomposed  by  heat. 

2.  Potash  produces  in  solutions  of  oxide  of  chromium, 
a  bluish  green  precipitate  of  HYDRATED  OXIDE  OF  CHROMIUM 
(Cr  2O3  +  HO)  which  easily  and  completely  redissolves 
in  an  excess  of  the  precipitant,  imparting  an  emerald-green 
colour  to  the  fluid.     If  this  solution    is  kept  constantly 
boiling  for  a  certain  time,  the  precipitate  completely  sepa- 
rates again,  so  that  the  supernatant  liquor  appears  perfectly 
colourless.     The  dissolved  hydrated  oxide  of  chromium  is 
also  precipitated,  if  the  potash  solution  is  mixed  with  hy- 
drochlorate of  ammonia  and  heated. 

3.  Ammonia  produces  the  same  precipitate  of  HYDRATED 
OXIDE  OF  CHROMIUM.     An  excess  of  the  precipitant  redis- 
solves  it  to  a  small  extent,  at  a  low  temperature,  but  the 
precipitation  is  complete,  if  the  solution  is  boiled  after  the 
addition  of  ammonia  in  excess. 

4.  If  oxide  of  chromium,  or  a  compound  of  this  sub- 
stance,  are  fused  together  with  nitre,  CHROMATE  OF  POT- 
ASH, (KO,  Cr  O  ,)  is  obtained  in  all  cases  ;  in  this  process 
a  portion  of  the  oxygen  of  the  nitric  acid  leaves  its  com- 


96  OXIDE    OF    2INC,   &C. 

bination,  and  forms  with  the  oxide  of  chromium,  chromic 
acid,  which  then  combines  with  the  potash  of  the  decom- 
posed saltpetre.  For  the  Reaction  of  Chromic  Acid,  vide 
infra,  §  95,  b. 

5.  Phosphate  of  soda  and  ammonia  dissolves  oxide  of 
chromium  and  its  salts,  as  well  in  the  oxidizing  as  in  the 
reducing  flame  of  the  blow -pipe,  giving  rise  to  the  forma- 
tion of  clear,  FEEBLY  YELLOWISH-GREEN  GLASS,  the  Colour 
of  which  changes  to  emerald-green,  on  cooling.  Borax 
manifests  a  similar  relation. 

Recapitulation  and  remarks. — The  solubility    of  the 
'chromium   and  alumina,  in  potash   and  their 
pre  from  potash  solutions,  by  means  of  hydro- 

ammonia,  allows  us,  in  the  first  place,  to  sepa- 
rate them  from  the  oxides  of  other  groups,  and  affords  us, 
in  the  second  place,  a  certain  means  of  detection  for 
alumina,  when  no  oxide  of  chromium  is  present.  If  the 
latter,  therefore,  is  present— which  we  may  ascertain  either 
by  the  colour  of  the  solution,  or,  at  any  rate,  by  the  re- 
action with  phosphate  of  soda  and  ammonia, — it  must  be 
separated  before  we  can  proceed  to  test  for  alumina.  This 
separation  may  be  effected  most  completely  by  fusing  the 
mixed  oxides  together  with  nitre.  The  precipitation  of 
oxide  of  chromium,  by  means  of  boiling  its  potash  solu- 
tion, is  also  a  sufficiently  exact  indication  j  it  gives,  how- 
ever, frequently  rise  to  mistakes. 

§  88. 
Fourth  Group. 

OXIDE  OF  ZINC,  PROTOXIDE  OF  MANGANESE,  OXIDE  OF 
NICKEL,  PROTOXIDE  OF  COBALT,  PROTOXIDE  OF  IRON, 
PEROXIDE  OF  IRON. 

Properties  of  the  group. — The  sulphurets  correspond- 
ing with  these  oxides,  are  more  or  less  soluble  in  dilute 
acids,  but  insoluble  in  water,  alkalies,  and  alkaline  sul- 
phurets. The  solutions  of  the  salts  of  these  oxides,  are, 
therefore,  not  at  all  precipitated  by  sulphuretted  hydrogen, 
when  they  contain  free  acid,  and  either  not  at  all,  or  at 
.  least  but  incompletely,  when  they  are  neutral,  but  com- 


OXIDE    OF    ZINC.  97 

pletely,  when  they  are  alkaline,  or  when  an  alkaline  sul- 
phuret  is  employed  instead  of  sulphuretted  hydrogen. 

Special  Reactions, 
a.   OXIDE  OF  ZINC.     (Zn  0.) 

1.  The  compounds  of  oxide  of  zinc  are  colourless.    Its 
soluble  neutral  salts*  redden  litmus  paper,  and  are  easily 
decomposed  by  heat,  with  the  exception  of  sulphate  of 
zinc,  which  can  bear  a  slight  degree  of  red  heat, 

2.  Sulphuretted    hydrogen   precipitates   from    neutral 
zinc  solutions,  a  portion  of  the  zinc  as  white  IURET 
OF    ZINC   (Zn  S.)      In   acid   solutions   no  ; 

formed,  if  the  free  acid  present  be  one  i  mger 

acids. 

3.  Hydrosulphuret   of    ammonia    throws   down   from 
neutral  as  sulphuretted  hydrogen  does  from  alkalirie  solu- 
tions, all  the  zinc  they  contain,  as  SULPHURET  OF  ZINC,  in 
the  form  of  a  white  precipitate.     This  precipitate  is  not 
redissolved  by  hydrosulphuret  of  ammonia  in  excess,  nor 
by  potash  or  ammonia  ;  it  is  sparingly  soluble  in  hydro- 
chloric acid,  but  easy  of  solution  in  aqua  regia. 

4.  Potash  and  ammonia  throw  down  from  solutions  of 
zinc,  HYDRATED  OXIDE  OF  ZINC  (Zn  Q,  HO)  in  the  form 
of  a  white  gelatinous  precipitate,  whicHls  easily  and  com- 
pletely redissolved  by  an  excess  of  the  precipitant. 

5.  Carbonate  of  potash  produces  a  precipitate  of  BASIC 
CARBONATE  OF  ZINC  3  (Zn  O,  HO)  +  2  (Zn  O,  CO2) 
which  is  insoluble  in  an  excess  of  the  precipitant.     The 
presence  of  salts  of  ammonia  prevents  its  formation,  or 
they  redissolve  it  when  already  formed,  giving  rise  to  the 
formation  of  double  salts  of  oxide  of  zinc  and  ammonia. 

6.  Carbonate  of  ammonia  produces  the  same  precipi- 
tate  as  carbonate   of  potash ;  addition   of  carbonate   of  < 
ammonia  in  excess  redissolves  it. 

7.  Oxide  of  zinc,  or  a  salt  of  oxide  of  zinc  mixed  with 
carbonate  of  soda,  and  exposed  to  the  reducing  flame  of 
the  blow-pipe,  covers  the  coal  support  with  an  incrustation 
of  OXIDE  OF  ZINC,  presenting  a  yellow  colour,  as  long  as  it 
is  hot,  and  changing  to  white,  on  cooling.     This  is  caused 
by  the  reduced  metallic  zinc  volatilizing  at  the  moment  of 


98  PROTOXIDE    OF  MANGANESE. 

its  reduction,  and  reoxidizing  in  passing  through  the  outer 
flame. 

8.  If  oxide  of  zinc,  or  a  salt  of  zinc,  be  moistened  with 
solution  of  protonitrate  of  cobalt,  and  heated  before  the 
blow-pipe,  an  unfused  beautifully  GREEN  coloured  mass  is 
obtained,  consisting  of  a  combination  of  oxide  of  zinc  with 
protoxide  of  cobalt. 


b.    PROTOXIDE    OF    MANGANESE.       (Mn  0.) 

1.  The  protosalts  of  manganese  are  colourless  or  of  a 

pale  red  ;  some  of  them  '  are   soluble,    others    insoluble. 

i  salts  are  decomposed  by  a  red  heat,  with  the 

f  protosulphate  of  manganese.     The  solutions 

yanese  salts  do  not  alter  vegetable  colours. 

retted  hydrogen  does  not  precipitate  acid  nor 
neutral  solutions  of  prototoxide  of  manganese. 

3.  Hydrosulphuret  of  ammonia  throws  down  from  neu- 
tral solutions,  as  sulphuretted  hydrogen  does  from  alkaline, 
all  the  manganese  they  contain,  as  SULPHURET  OF  MANGA- 
NESE (Mn  S)  in  the  form  of  a  bright  flesh-coloured  preci- 
pitate, which  changes  to  a  dark-brown  when  exposed  to 
the  air  ;  this  precipitate  is  insoluble  in  hydrosulphuret  of 
ammonia  and  in  alkalies,  but  easily  soluble  in  hydrochloric 
acid  and  nitric  acid. 

4.  Potash  aiid^mmonia  produce  whitish  precipitates  of 

HYDRATED     PROTOXIDE     OF      MANGANESE,     (Mn     O,     HO,) 

which,  when  exposed  to  the  air,  soon  change  to  a  brownish, 
and  at  last,  to  a  dark  blackish  brown  colour,  owing  to  the 
hydrated  protoxide  being  converted  into  hydrated  peroxide, 
by  the  absorption  of  oxygen  from  the  air.  Ammonia  and 
carbonate  of  ammonia  do  not  redissolve  this  precipitate  ; 
but  sal  ammoniac  prevents  the  precipitation  by  ammonia 
completely,  and  that  by  potash  partly.  Solution  of  sal 
ammoniac  redissolves  only  those  parts  of  the  already- 
formed  precipitates  which  have  not  yet  undergone  a  higher 
degree  of  oxidation.  The  solution  of  the  hydrated  protox- 
ide in  sal  ammoniac  depends  on  the  disposition  of  the  pro- 
tosalts of  manganese  to  form  double  salts  with  salts  of 
ammonia.  The  pellucid  solutions  of  these  double  salts 
become  brown,  when  exposed  to  the  air,  and  depose  dark- 
brown  peroxide  of  manganese. 


'.  OXIDE   OF   NICKEL.  99 

5.  If  any  compound  of  manganese  be  fused  with  car- 
bonate  of  soda,  on  a  platinum  wire,  in  the  outer  flame, 
MANGANATE  OF  SODA   is  formed,  which  makes  the   test 
specimen  appear  GREEN,  as  long  as  it  is  hot.  but,  after 
cooling,   of  a  bluish  green   and  opaque.     This  reaction 
enables  us  to  detect  the  smallest  quantities  of  manganese. 
The  delicacy  of  the  test  is  still  further  increased  if  a  minute 
quantity  of  nitre  is  added  to  the  carbonate  of  soda. 

6.  Borax  and  phosphate  of  soda   and  ammonia   dis- 
solve manganese   compounds,  in  the  outer  flame  of  the 
blow-pipe,  giving  rise  to  the  formation  of  clear  and  VIOLET- 
RED   glasses,  which,  on  cooling,  appear  of  an   amethyst 
red,  and  lose  their  colour  when  exposed  to  the  inner  flame, 
owing  to  the  peroxide  becoming  reduced  to  proton 

glass  which  borax  forms  with  manganese,  appears  black 
when  containing  a  considerable  proportion  of  peroxide  of 
manganese,  but  the  glass  formed  by  phosphate  of  soda 
and  ammonia  never  loses  its  transparency.  The  latter, 
when  exposed  to  the  inner  flame,  becomes  colourless  far 
more  easily  than  the  former. 

C.    OXIDE    OF  NICKEL.       (Ni   O.) 

1.  The    salts   of   nickel   are    yellow   or   green  ;  their 
solutions    are    of   a  bright   green    colour.     The   soluble 
neutral  salts  redden  litmus  paper  and  are  decomposed  at  a 
red  heat. 

2.  Sulphuretted  hydrogen  precipitates  neither  acid  nor" 
neutral  solutions  of  nickel ;  or  the  latter  at  least  but  very 
incompletely. 

3.  Hydrosulphuret  of  ammonia  produces  in  neutral,  as 
sulphuretted  hydrogen  does  in  alkaline  solutions,  a  black 
precipitate  of  SULPHURET  OF  NICKEL,  (Ni  S,)  which  is  not 
altogether  insoluble  in  hydrosulphuret  of  ammonia,  owing  to 
which  property  the  fluid  from  which  it  has  been  precipita- 
ted, presents   always   a  brownish  colour.     Sulphuret  of 
nickel  is  dissolved  with  difficulty  by  hydrochloric  acid,  but 
easily  by  aqua  regia. 

4.  Potash  produces   a    bright    green    precipitate    of 
HYDRATED  OXIDE  OF  NICKEL,  (Ni  O,  HO,)  which  is  insolu- 
ble  in  potash,  and  does  not  alter  when  exposed  to  the  air. 
Carbonate  of  ammonia  re-dissolves  this  precipitate  to  a 


100  PROTOXIDE    OF    COBALT. 

greenish-blue  fluid,  from  which  potash  again  precipitates 
the  nickel  it  contains,  as  a_  yellow-green  hydrated  oxide  of 
nickel. 

5.  Ammonia  precipitates    also    HYDRATED    OXIDE    OF 
NICKEL,  but  an  excess  of  the  precipitant  easily  re-dissolves 
it  to  a  blue  fluid,  as  a  double  salt  of  oxide  of  nickel  and 
ammonia.     Potash  precipitates  hydrated  oxide   of  nickel 
from  this  solution. 

6.  Cyanide  of  potassium   produces  a  yellowish-green 
precipitate  of  CYANIDE  OF  NICKEL,  (Ni  Cy,)  which  by  an 
excess  of  the  precipitant  is  easily  redissolved  to  a  brownish- 
yellow  fluid,  containing  cyanide  of  nickel  and  cyanide  of 
potassium  combined.  Sulphuric  acid  and  hydrochloric  acid 
again   precipitate    from    this    solution  cyanide  of  nickel, 
which  is  very  difficultly  soluble  in  an  excess  of  these  acids, 
at  a  low  temperature, 

7.  Borax  and  phosphate  of  soda  and  ammonia  dissolve 
compounds  of  oxide  of  nickel,  in  the  outer  flame  of  the 
blow-pipe,  giving  rise  to  the  formation  of  clear  glasses  of  a 
dark  yellow  colour?  with  a  tinge  of  red-brown,  which  become 
clearer  and  almost  colourless  on  cooling.     Addition  of  nitre 
or  carbonate  of  potash  changes  the  colour  to  blue  or  to  dark 
purple.     The  glass  which  phosphate  of  soda  and  ammonia 
forms  with  nickel  remains  unaltered  when  exposed  to  the 
inner  flame,  but  that  of  borax  bepomes  grey  and  troubled 
owing  to  the  reduction  of  nickel. 

d.    PROTOXIDE    Or    COBALT.  (Co  O,) 

1.  The  protosalts  of  cobalt  are  blue  in  their  anhydrous, 
and  of  a  characteristic  bright  red  tint  in  their  hydrated  state. 
Their  solutions  show  their  colour  even  when  considerably 
diluted.     The  soluble  neutral  salts  redden  litmus  paper, 
and  are  decomposed  by  a  red  heat. 

2.  Sulphuretted  hydrogen  does  not  precipitate  acid  so- 
lutions of  cobalt,  and  neutral  solutions  at  the  most,  very 
incompletely,  when  they  contain  weak  acids  ;  these  latter 
precipitates  are  of  a  black  colour. 

3.  Hydrosulphuret  of  ammonia  precipitates  from  neutral, 
as  sulphuretted  hydrogen  do  esfrom  alkaline  solutions,  all 
the  cobalt  they  contain,  as  black  SULPIIURET  OF  COBALT. 


PEROTOXIB&  OT  JjROtf- _    ,     ^     ,     ,  ^         101 

(Co  S.)  This  substance  is  insoluble  in  alkalies" and  hydro- 
sulphuret  of  ammonia,  difficultly  soluble  in  hydrochloric 
acid,  easily  soluble  in  aqua  regia. 

4.  Potash  produces  in  solutions  of  cobalt  BLUE  precipi- 
tates of  basic  salts  of  cobalt,  which  become  GREEN  when 
exposed  to  the  air,  owing  to  the  absorption  of  oxygen,  and 
are  converted  into  hydrates  of  a  jjale   red   colour  when 
boiled.     They  are  insoluble  in  potash.     But  neutral  car- 
bonate of  ammonia  dissolves  them  completely  to  intensely 
violet-red  fluids,  in  which  potash  does  not  cause  any,  or,  at 
least,  but  a  very  scanty  precipitate. 

5.  Ammonia  produces  the  same  precipitate  as  potash, 
but  an  excess  of  the  precipitant  redissolves  it  to  a  reddish- 
brown  fluid,  in  which  potash  does  not  cause  any,  or  aUeast 
but  a  very  scanty,  precipitate. 

6.  If  to  a  solution  of  cobalt  acidified  with  some  hydro- 
chloric acid,  cyanide  of  potassium  be  added,  a  brownish- 
white  precipitate  of  PROTOCYANIDE  OF  COBALT  is  formed, 
which  by  an  excess  of  the  precipitant,  with  presence    of 
free  hydrocyanic  acid,  is  easily  dissolved  to  COBALTOCYA- 
NIDE  OF  POTASSIUM.     (Cy6  Co2+3K.)     Acids  cause  no 
precipitation  in  the  solutions  of  this  salt. 

7.  Borax  dissolves  compounds  of  cobalt  in  the  inner  as 
well  as   in   the   outer  flame   of  the  blow-pipe,  TO  CLEAR 
SPLENDIDLY  BLUE  COLOURED  GLASSES  which  appear  almost 
black,  when  cobalt  is  present  in  any  considerable  propor- 
tion.    This  test  is  as  delicate  as  it  is  characteristic.  Phos- 
phate of  soda  and  ammonia  manifest  the  same   reaction, 
but  in  a  lesser  degree. 

€.    PROTOXIDE  OF  IRON.       (Fe  O.) 

1.  The  protosalts  of  iron  have  a  greenish  colour  ;  their 
solutions  appear  coloured  only  when  quite  concentrated. 
The  soluble  neutral  salts  redden  litmus  paper  and  are  de- 
composed by  a  red  heat. 

2.  Acid  solutions  are  not  precipitated  by  sulphuretted 
hydrogen,  and  neutral  solutions,  with  weak  acids,  at  the 
most  but  incompletely.    These  precipitates  are  of  a  black 
colour. 

3.  Hydrosulphuret  of  ammonia  precipitates  from  neu- 
tral, as  sulphuretted  hydrogen  does  from  alkaline  solutions, 


102  £ERpX!DE    OP   IRON. 


all  °the  iron  they  contain,  as  black  SULPHURET  OP  IRON, 
(Fe  S,)  which  is  insoluble  in  alkalies  and  alkaline  sul- 
phurets,  but  easy  of  solution  in  hydrochloric  acid  and  nitric 
acid. 

4.  Potash  and  ammonia  produce  a  precipitate  of  HY- 
DRATED  PROTOXIDE  OF  IRON,  (Fe  O,  HO,)  which,  in  the 
first  moment,  appears^lmost  white,  but,  after  a  very  short 
time,  becomes  of  a  dirty  green,  by  absorption  of  oxygen  from 
the  air,  and  at  last  assumes  a  red-brown  colour.  The 
presence  of  salts  of  ammonia  prevents  the  precipitation  by 
potash  partly,  and  that  by  ammonia  totally. 

Verrpcyanide  of  potassiun  produces  in  solutions  of 
protoxide  of  iron  a  bluish-white  precipitate  of  FERROCYA- 
NIDB  OF  POTASSIUM  AND  IRON,  (2  Cfy+K+3  Fe,)  which,  by 
absorption  of  oxygen  from  the  air,  soon  becomes  blue.  In 
this  change,  all  the  potassium  of  three  equivalents  of  the 
compound,  and  one  equivalent  of  iron,  become  oxidized, 
and  Prussian  blue  (3  Cfy+2  Fe2)  remains.  Nitric  acid 
or  chlorine  causes  this  oxidation  immediately. 

6.  Ferricyanide  of  potassium  produces   a  splendidly 
blue  precipitate  of  FERRICYANIDE  OF  IRON,  (2  Cfy-f-3  Fe.) 
This  precipitate  does  not  differ   in  colour  from  Prussian 
blue.     It  is  insoluble  in  hydrochloric  acid,  but  easily  de- 
composed by  potash.     When  the  solution  of  protosalt  of 
iron  is  highly  dilute,  the  reagent  imparts  to  it  only  a  dark 
bluish  green  colour. 

7.  Borax  dissolves  protosalts  of  iron  in  the  oxidising 
flame,  forming  DEEP  RED  GLASSES,  the  colour  of  which 
changes  to  bottle  'green  when  exposed  to  the  inner  flame, 
owing  to  the   reduction  of  the  first  formed  peroxide    to 
magnetic-oxide.     Both  tints  disappear  totally,  or  in  a  great 
measure,  when  the  glasses  become  cool.     Phosphate  of 
soda  and  ammonia  shows  a  similar  relation  to  the  proto- 
salts of  iron,  but  the  colour  of  its  glass  vanishes  even  more 
decidedly  than  is  the  case  with  borax. 

/.  PEROXIDE    OF    IRON.       (Fea    O3.) 

1.  The  persalts  of  iron  are  of  a  more  or  less  red  yel- 
low colour.  Their  solutions  present  this  colour  even 
when  pretty  highly  diluted.  The  soluble  neutral  salts 
redden  litmus  paper  and  are  decomposed  by  heat. 


PEROXIDE    OF   IRON.  103 

/  2.  Sulphuretted  hydrogen  produces  in  neutral  and  acid 
solutions  a  slight  precipitate  of  SULPHUR,  which  renders  the 
solution  turbid  and  imparts  a  milky  white  tint  to  it.  Pe- 
roxide of  iron  and  sulphuretted  hydrogen  decompose  each 
other ;  in  this  process  the  hydrogen  withdraws  from  the 
peroxide  of  iron,  one-third  of  its  oxygen  combining  with  it 
to  form  water  ;  the  persalt  of  iron  is  thus  converted  into  a 
protosalt,  and  the  sulphur  of  the  decomposed  sulphuretted 
hydrogen  separates. 

3.  Hydrosulphuret  of  ammonia  precipitates  from  neu- 
tral, as  sulphuretted  hydrogen  does  from  alkaline  solutions, 
all  the  peroxide  of  iron  they  contain,  as  black  SULPHURET 
OF  IRON  ;  this  precipitation  is  preceded  by  the  conversion 
of  the  persalt  into  a  protosalt.     The  reagent  produces  only 
a  blackish-green  tint  in  the  fluid,  if  the  solution  is  very 
dilute.     The  minutely  divided  sulphuret  of  iron  subsides 
in  such  cases  only  after  the  lapse  of  some  time.     For  the 
several  degrees  of  solubility  of  sulphuret  of  iron  in  vari- 
ous substances,  vide  e.  (Protoxide  of  iron.)  3. 

4.  Potash  and  ammonia  produce  bulky  red  brown  pre- 
cipitates of  HYDRATED  PEROXIDE  OF  IRON,  which  are  inso- 
luble  in  an  excess  of  the  precipitant,  as  well  as  in  salts  of 
ammonia. 

/      5.  Ferocyanide  of  potassium  produces  even  in  highly 
-  /  dilute  solutions  a  splendidly  blue  precipitate  of  SESQUIFER- 
/    ROCYANIDE  OF  IRON,  (3  Cfy~h4  Fe,)  (Prussian  blue)  which . 
is  insoluble  in  hydrochloric  acid,  but  easily  decomposed 
^    by  potash,  with  precipitation  of  peroxide  of  iron. 

6.  Ferricyanide  of  potassium  imparts  a  reddish-brown 
tint  to  solutions  of  peroxide  of  iron,  but  it  causes  no  pre- 
cipitate. 

7.  The  per  salts  of  iron  present  the  same  appearances  as 
the  protosalts,  when  exposed  to  the  action  of  the  blow-pipe 
flame,  vide  e.  (Protoxide  of  iron)  7. 

Recapitulation  and  remarks. — Of  the  metallic  oxides 
belonging  to  the  fourth  group,  oxide  of  zinc  alone  is  soluble 
in  potash.  It  is  this  property  which  distinguishes  it  from 
the  other  oxides  of  this  group,  and  connects  it  with  those 
of  the  third  group.  But  it  differs  from  oxide  of  chromium 
and  from  alumina,  inasmuch  as  sulphuretted  hydrogen 
precipitates  it  from  its  solutions  in  potash.  This  charac- 
teristic property  is  the  surest  test  of  oxide  of  zinc.  Pro- 


104  PEROXIDE  OF  IROIf. 

toxide  of  manganese,  oxide  of  nickel,  protoxide  of  cobalt, 
and  protoxide  of  iron  form  with  salts  of  ammonia  double 
salts,  from  which  the  metallic  oxides  are  not  precipitated 
by  free  ammonia  ;  but  peroxide  of  iron,  just  like  the  oxides 
of  the  third  group,  is  completely  precipitated  by  ammonia, 
even  when  salts  of  ammonia  are  present.  Hence  it  follows, 
in  the  first  place,  that  by  means  of  this  property,  manganese, 
nickel  and  cobalt  may  be  separated,  as  well  from  peroxide 
of  iron  as  from  oxide  of  chromium  and  from  alumina  ;  and, 
in  the  second  place,  that,  in  order  to  separate  these  metals 
from  protoxide  of  iron,  the  latter  substance  must  first  be 
peroxidized,  which  operation  is  best  performed  by  boiling 
its  solution  with  nitric  acid.  The  peroxide  of  iron  differs 
from  oxide  of  chromium,  and  from  alumina,  inasmuch  as  it 
is  insoluble  in  potash  ;  and  peroxide  of  iron  may  be  distin- 
guished from  protoxide,  by  means  of  ferrocyanide  of  potas- 
sium. Hydrated  oxide  of  nickel  and  hydrated  protoxide  of 
cobalt  dissolve  in  carbonate  of  ammonia,  whilst  hydrated 
protoxide  of  manganese  is  insoluble  in  this  substance.  We 
may,  therefore,  by  means  of  this  solvent,  separate  the  pro- 
toxide of  manganese  from  the  two  other  oxides.  The 
brown  tint  assumed  by  the  white  hydrated  protoxide  when 
exposed  to  the  air,  and  the  blow-pipe  reactions,  especially 
that  with  soda,  are  the  surest  test  of  protoxide  of  manga- 
nese. Cyanide  of  nickel,  and  cyanide  of  cobalt  are  soluble 
in  cyanide  of  potassium.  But  cyanide  of  nickel  may  be 
precipitated  from  this  solution  by  acids,  which  is  not  the 
case  with  cyanide  of  cobalt.  This  property,  i.  e.  the  for- 
mation of  a  precipitate  in  a  solution  of  these  two  cyanides 
in  cyanide  of  potassium,  by  the  addition  of  hydrochloric 
acid,  is,  under  all  circumstances,  a  perfectly  sure  test  of 
the  presence  of  nickel.  Whether  this  precipitate  be  cyanide 
of  nickel  or  cobalticyanide  of  nickel,  is  quite  immaterial 
as  far  as  the  detection  of  nickel  is  concerned ;  we  have 
only  to  bear  in  mind  that  no  precipitate  forms  if  cobalt 
alone  be  contained  in  the  solution,  since  cobalticyanide  of 
potassium  is  not  decomposed  by  hydrochloric  acid.  To 
explain  the  composition  of  the  precipitates  formed,  and  the 
process  in  general,  we  will  now  proceed  to  consider  and 
examine  three  special  cases,  the  difference  of  which  de- 
pends on  the  unequal  relative  proportion  of  the  nickel  and 
the  cobalt. 


PEROXIDE  or  IRON.  105 

X  Ni  :  Co  =  3  eq.  :  2  eq. 

2,  Ni  :  Co  =  3  eq.  :  2  eq.+x 

3,  Ni  :  Co  =  3  eq.  +  x  :  2  eq. 

Consequently,  we  get  in  solution  in  the  first  case,  one  eq. : 
of  cobalticyanide  of  potassium,    (Cy6,  Co2  +  3  K,)  and 
3  eq. :  of  cyanide  of  nickel  and  cyanide  of  potassium  com- 
bined, (Cy3  Ni,  +  Cy3  K,)  and  if  we  add  hydrochloric  acid 
in  excess  to  this  solution,  we  obtain  a  dirty  green  precipi- 
tate of  cobalticyanide  of  nickel,  (Cy6  Co2+3  Ni,)  which 
contains  all  the  nickel  and  cobalt  of  the  solution  ;  in  this 
process  the  combination  of  cyanide  of  nickel  and  cyanide 
of  potassium  is  decomposed,  and  the  potassium  in  the  co- 
balticyanide of  potassium  changes  places  with  the  nickel 
in  the  cyanide  of  nickel.     Besides  the  cobalticyanide  of 
nickel,  chloride  of  potassium  and  hydrocyanic  acid  are 
formed.     In  the  second  case  we  obtain  also  a  precipitate  of 
cobalticyanide  of  nickel,  but  this  precipitate,  though  con- 
taining all  the  nickel,  does  not  contain  all  the  cobalt  of  the 
solution,  for  the  excess  of  cobalticyanide  of  potassium  is 
not  decomposed.    In  the  third  case,  at  last,  we  obtain  a  pre- 
cipitate of  cobalticyanide  of  nickel,  which  contains  all  the 
cobalt  and  a  portion  of  the  nickel,  mixed  with  insoluble 
cyanide  of  nickel,  which  contains  the  remaining  part  of 
the  nickel.    The  precipitate  of  cobaltcyanide  of  nickel  has 
been  formed,  as  in  the  first  case,  whilst  the  cyanide  of 
nickel  is  formed  by  the  decomposition  of  the  double  cy- 
anide of  nickel  and  potassium  in  excess.     Hence  it  is  evi- 
dent, that  nickel  is,  in  all  cases,  a  necessary  condition  to 
the  formation  of  a  precipitate,  and  consequently  that  this 
precipitate  can  leave  no  doubt  as  to  its  presence.    As  co- 
balt may,  under  all  circumstances,  be  safely  and  easily 
detected  by  its  characteristic  properties  before  the  blow- 
pipe,  any  further  indications  for  the   mere  detection  of 
either  metal,  would  almost  seem  superfluous  ;  but  since 
we  are  now  already  far  advanced  towards  the   complete 
separation  of  these  two  substances  from  each  other,  we 
may  as  well  briefly  state  how  to  effect  it.     In  the  first  and 
second  of  the  above-mentioned  cases,  we  have,  after  the  ad- 
dition of  the  hydrochloric  acid,  only  to  heat  the  fluid  to- 
gether with  the  therein  suspended  precipitate  of  cobalti- 
cyanide of  nickel,  till  the  free  hydrocyanic  acid  is  expelled, 


106  OXIDE    OF    SILVER,  &C. 

(the  cobalticyanide  of  nickel  as  well  as  the  cobalticyanide 
of  potassium  present  in  the  second  case,  remain  unaltered 
during  this  operation  ; )  and  then  we  may,  by  addition  of 
caustic  potash,  easily  decompose  the  cobalticyanide  of 
nickel,  into  cobalticyanide  of  potassium,  which  remains  in 
solution,  and  oxide  of  nickel  which  precipitates  as  hy- 
drated  oxide.  But  in  the  third  case  we  must  add  a  larger 
quantity  of  hydrochloric  acid,  and  boil  the  solution  there- 
with, till  the  cyanide  of  nickel  contained  in  the  precipitate 
(which  would  only  be  incompletely  decomposed  by  pot- 
ash) is  converted  into  chloride  of  nickel,  and  till  the  hy- 
drocyanic acid,  formed  during  this  operation,  is  completely 
expelled  ;  and  then,  after  this  preparatory  process,  we 
may,  by  boiling  with  caustic  potash,  obtain  all  the  nickel 
as  an  insoluble  hydrated  oxide,  and  all  the  cobalt  as  soluble 
cobalticyanide  of  potassium.  Lastly,  we  must  still  men- 
tion, that  the  oxides  of  the  fourth  group  are  not  precipi- 
tated by  alkalies,  if  non-volatile  organic  substances,  (such 
as  sugar,  tartaric  acid,  &c.)  are  contained  in  their  solu- 
tions. The  same  is  the  case  with  alumina  and  oxide  of 
chromium. 

§  89. 
Fifth  Group. 

OXIDE  OF  SILVER,  PROTOXIDE  OF  MERCURY,  PEROXIDE  OF 
MERCURY,  OXIDE  OF  LEAD,  OXIDE  OF  BISMUTH,  OXIDE  OF 
COPPER,  OXIDE  OF  CADMIUM. 

Properties  of  the  group. — The  sulphurets  correspond- 
ing with  the  oxides  of  this  group,  are  insoluble  both  in 
dilute  acids  and  in  alkaline  sulphurets.  The  solutions  of 
these  oxides  are,  therefore,  completely  precipitated  by 
sulphuretted  hydrogen,  no  matter  whether  their  reaction  be 
neutral,  alkaline,  or  acid. 

We  divide  the  oxides  of  this  group  into  two  sections, 
and  distinguish 

1.  OXIDES  PRECIPITABLE  BY  HYDROCHLORIC    ACID,  viz.  I 

oxide  of  silver,  protoxide   of  mercury,  and   oxide  of  lead, 
from 

2.  OXIDES,  NOT  PRECIPITABLE  BY  HYDROCHLORIC  ACID, 
ivz. :  peroxide  of  mercury,  oxide  of  copper,  oxide  of  bis- 


OXIDE    OP    SILVER.  107 

muth,  oxide  of  cadmium.  Lead  must  be  considered  in 
both  sections,  as  the  difficult  solubility  of  its  chloride 
renders  it  possible  to  confound  it  with  protoxide  of  mer- 
cury and  oxide  of  silver,  without  affording  us  .any  means  of 
separating  it  completely  from  the  oxides  of  the  second 
section. 

§  90. 

FIRST  SECTION.       OXIDES  PRECIPITABLE  BY  HYDROCHLORIC 

ACID. 

Special  Reactions. 

a.      OXIDE     OF    SILVER.       (Ag  0.) 

1.  The  salts  of  oxide  of  silver  are  fixed  and  colourless  ; 
most  of  them  blacken  when  exposed  to  light.    The  soluble 
neutral  salts  do  not  alter  vegetable  colours,  and  are  decom- 
posed at  a  red  heat. 

2.  Sulphuretted  hydrogen  and   hydrosulphuret  of  am- 
monia precipitate  black   SULPHURET  OF  SILVER,  (Ag  S,) 
which  is  insoluble  in  dilute  acids,  alkalies,  alkaline  sul- 
phurets,  and  cyanide  of  potassium.     Boiling  concentrated 
sulphuric  acid  easily  decomposes  and  dissolves  this  pre- 
cipitate, with  separation  of  sulphur. 

3.  Potash  and  ammonia  precipitate  OXIDE  OF  SILVER,  in 
the  form  of  a  BRIGHT  BROWN  powder,  which  is  insoluble 
in  potash,  but  easy  of  solution  in  ammonia.  The  presence 
of  salts  of  ammonia  prevents  this  reaction  either  totally  or 
partly. 

4.  Hydrochloric  acid  and  soluble  chlorides  produce  a 
white  curdy  precipitate  of  CHLORIDE  OF  SILVER.     (Ag  Cl.) 
In  very  dilute  solutions,  this  precipitate  merely  imparts  to 
the  fluid  a  bluish  white  opalescent  appearance.  The  white 
chloride  of  silver,  when  exposed  to  light,  acquires  first  a 
violet  tint,  and  at  last  a  black  colour,  but  without  any  alter- 
ation in  its  composition ;  it  is  insoluble  in  nitric  acid,  but 
dissolves  easily  in  ammonia,  giving  rise  to  the  formation  of 
chloride  of  silver  and  ammonia.    Acids  precipitate  it  again 
from  this  combination.     Chloride  of  silver,  when  heated, 
fuses  without  decomposition,  forming  a  transparent  horny 
mass. 


108  PROTOXIDE    OP    MERCURY. 

5.  When  silver  compounds,  mixed  with  carbonate  of 
soda,  are  on  a  charcoal  support,  exposed  to  the  inner 
flame  of  the  blow-pipe,  WHITE,  SHINING,  AND  DUCTILE 
METALLIC  GLOBULES  are  obtained,  whilst  no  incrustation 
takes  place. 

b.    PROTOXIDE    OF    MERCURY.       (Hg2    0.) 

1.  The  salts  of  protoxide  of  mercury,  when  exposed  to 
a  red  heat,  either  volatilize  without  decomposition,  or  de- 
compose ;  in  the  latter  case  the  mercury  separated  volatili- 
zes in  a  metallic  state.  They  are  colourless.     The  soluble 
salts,  when  neutral,  redden  litmus  paper ;    when  mixed 
with  much  water,  they  separate  into  insoluble  basic  and 
soluble  acid  salts- 

2.  Sulphuretted  hydrogen  and  hydrosulphuret  of  am- 
monia produce  black  precipitates  of  SULPHURET  OF  MER- 
CURY, (Hg2  S,)  which  are  insoluble,  as  well  in  dilute  acids 
as  in  alkaline  sulphurets,  and  in  cyanide   of  potassium. 
Potash  resolves  this  sulphuret  into  bisulphuret  and   glo- 
bules of  metallic  mercury.   Sulphuret  of  mercury  is  easily 
decomposed  and  dissolved  by  aqua  regia,  but  not  by  boil- 
ing concentrated  nitric  acid. 

3.  Potash    and   ammonia    produce  black  precipitates, 
which  are  insoluble  in  an  excess  of  the  precipitants.   The 
potash  precipitates  consist  of  PROTOXIDE   OF  MERCURY  ; 
those  of  ammonia,  of  BASIC  SALT  OF  PROTOXIDE  OF  MER- 
CURY  AND    AMMONIA. 

4.  Hydrochloric  acid  and   soluble  chlorides  precipitate 
PROTOCHLORIDE  OF  MERCURY  (Hg2  Cl)  as  a  shining  white, 
fine   powder.     Cold    hydrochloric  acid,  and   cold  nitric 
acid,  do  not  dissolve  this  precipitate  ;  but  it  dissolves,  al- 
though very  difficultly  and  slowly,  when  long  boiled  with 
these  acids,  being  converted  by  hydrochloric   acid   into 
chloride  of  mercury,  by  nitric  acid  into  chloride  of  mercury 
and  per-nitrate  of  mercury.     Ammonia  and  potash  decom- 
pose protochloridc  of  mercury,  giving  rise  to  the  forma- 
tion of  black  protoxide  of  mercury. 

5.  If  a  drop  of  a  neutral  or  feebly  acid  solution  of  prot- 
oxide of  mercury  be  poured  on  a  clean  and  smooth  surface 
of  copper,  washed  off  after  some  time,  and  the  spot  rubbed 
with  cloth  or  paper,  &c.  &c.,  it  will  appear  of  a*  SILVERY 


OXIDE    OP    LEAD.  109 

WHITE  COLOUR,  with  metallic  lustre.  This  apparent  sil- 
vering vanishes  when  the  copper  is  heated,  owing  to  the 
volatilization  of  the  metallic  mercury  precipitated  on  its 
surface. 

6.  Protochloride  of  tin  produces  in  solutions  of  prot- 
oxide of  mercury,  a  gray  precipitate  of  METALLIC  MER- 
CURY, which  may  be  united  into  globules  by  heating  and 
agitating  it,  but  most  easily  by  boiling  it  with  hydrochloric 
acid. 

7.  If  mercury  compounds,  intimately  mixed  with  efflor- 
esced carbonate  of  soda,  and  covered   with    a  layer  of 
carbonate  of  soda  in  a  distended  glass-tube,   are  heated 
before  the  blow-pipe,  a  decomposition  always  takes  place 
to  the  effect  of  liberating  metallic  mercury,  which  sublimes 
as  a  gray  crust  above  the  heated  part  of  the  tube.     The 
fine  particles  of  mercury  unite  into  globules  on  this  crust 
being  rubbed  with  a  glass  rod. 

C.    OXIDE    OF  LEAD.    (Pb    O.) 

1.  The  salts  of  oxide  of  lead  are  colourless  and  not 
volatile ;  the  soluble  salts,  when  neutral,   redden  litmus 
paper,  and  are  decomposed  at  a  red  heat. 

2.  Sulphuretted  hydrogen  and  hydrosulphuret  of  am- 
monia produce  black  precipitates  of  SULPHURET  OF  LEAD, 
(Pb.S,)  which  are  insoluble  in  dilute  acids,  alkalies,  alka- 
line sulphurets,  and  cyanide  of  potassium.     This  sulphuret 
of  lead  is  decomposed  by  boiling  concentrated  nitric  acid  ; 
all  the  lead  is  first  converted   into  nitrate  of  lead,   the 
greater  portion  of  the  sulphur  separates,  another  portion  is 
converted  into  sulphuric  acid,  and  this  again  decomposes 
a  part  of  the  nitrate  of  lead^  and  thus,  besides  the  precipi- 
tated  sulphur,  sulphate  of  lead  is  formed,   and  remains 
undissolved  as  a  white  powder. 

3.  Potash  and  ammonia  throw  down  BASIC  SALT   OF 
LEAD  in  the  form  of  white  precipitates,  which  are  insolu- 
ble in  ammonia,  and  of  difficult  solution  in  potash. 

4.  Hydrochloric  acid  and  soluble  chlorides  produce  in 
concentrated  solutions  heavy  white  precipitates  of  CHLO- 
RIDE OF  LEAD,  (Pb  Cl,)  which  are  soluble  in  much  water, 
especially  if  the  water  be  heated.     This  chloride  of  lead 

5 


110  OXIDE    OF  LEAD. 

is  not  altered  by  ammonia,  and  is  more  difficult  of  solution 
in  hydrochloric  acid  and  in  nitric  acid  than  in  water. 

5.  Sulphuric  acid  and  sulphates  produce  white  preci- 
pitates of  SULPHATE   OF   LEAD,  (Pb  O,  SO3,)  which  are 
almost  insoluble  in  water  and  dilute  acids,  but  to  a  small 
extent  soluble  in  concentrated  nitric  acid,  difficult  of  solu- 
tion in  boiling  concentrated  hydrochloric  acid,  and  more 
easily  soluble  in  solution  of  potash.     Salts  of  ammonia? 
and  especially  sulphate  of  ammonia,  prevent  the  precipita- 
tion partly  or  altogether. 

6.  Chromate  of  potash  produces  a  yellow  precipitate  of 
CHROMATE  OF  LEAD,  (Pb  O,  Cr  O3)  which  is  easilysolu- 
ble  in  potash,  but  insoluble  in  dilute  nitric  acid. 

7.  Lead  compounds,  mixed  with  carbonate  of  soda,  and 
on  a  charcoal  support,  exposed  to  the  reducing  blow-pipe 

flame,  very  easily  yield  soft  and  ductile  METALLIC  GLO- 
BULES ;  whilst  the  coal  is,  at  the  same  time,  covered  with 
a  YELLOW  incrustation  of  OXIDE  OF  LEAD. 

Recapitulation  and  remarks. — The  metallic  oxides  of 
the  first  section  of  the  fifth  group  are  the  most  easily  cha- 
racterized in  their  corresponding  chlorides,  since  the 
divers  relations  of  these  different  chlorides  to  ammonia 
afford  us  means  as  well  of  detecting  as  of  separating  them 
from  each  other.  For  chloride  of  silver,  as  we  have  stated, 
is  dissolved  by  ammonia,  whilst  protochloride  of  mercury 
and  chloride  of  lead  remain  undissolved.  By  adding  nitric 
acid  to  a  solution  of  chloride  of  silver  and  ammonia,  we 
may  again  precipitate  the  chloride  of  silver ;  and  as  this 
reaction  admits  of  no  mistake,  we  want  in  fact  no  further 
means  for  the  detection  of  silver.  Of  the  two  remaining 
chlorides,  the  protochloride  of  mercury  is  converted  by 
ammonia  into  black  protoxide  of  mercury,  whilst  the  chlo- 
ride of  lead  remains  unaltered.  The  new-formed  protoxide 
of  mercury  may  be  separated  from  the  chloride  of  lead  by 
treating  with  nitric  acid,  whereby  the  protoxide  of  mercury 
is  dissolved ;  or  by  boiling  with  water,  when  solution  of 
the  chloride  of  lead  takes  place.  These  relations  suffi- 
ciently characterize  the  protoxide  of  mercury  ;  as  further 
tests  for  lead,  its  reaction  with  sulphuric  acid  or  with 
chromate  of  potash  may  be  employed. 


PEROXIDE    OF    MERCURY.  Ill 

§    91. 

SECOND    SECTION    OF    THE    FIFTH    GROUP.       OXIDES    WHICH 
ARE  NOT  PRECIPITATED  BY  HYDROCHLORIC  ACID. 

Special  Reactions. 

a.    PEROXIDE    OF    MERCURY.       (Hg  O.) 

1.  The  salts  of  peroxide  of  mercury  volatilize  when 
heated  to  redness,   some  with,  some  without  decomposi- 
tion.    Most  of  them  are  colourless.     The  neutral  soluble 
salts  redden  litmus  paper.     The  nitrate  and  sulphate  of 
peroxide  of    mercury   are    decomposed    by  much  water 
into  soluble  acid  and  insoluble  basic  salts. 

2.  If  sulphuretted  hydrogen^  or  hydrosulphuret  of  am- 
monia,  be  added  in  very  small  proportions  to  solutions 
of  peroxide  of  mercury,  and  these  solutions  be  then  agi- 
tated, a   perfectly  white   precipitate    is    obtained.     The 
addition  of  somewhat  large  quantities  of  these  reagents 
causes  the    precipitate  to  acquire   a  yellow,   orange,   or 
brown-red  colour,  as  more  or  less  of  them  is  added  ;  an 
excess  of  the  precipitate  produces  a  black  precipitate  of 

BISULPHURET    OF    MERCURY,     CINNABAR.         (Hg   S.)       This 

variation  of  colour  depends  on  the  different  proportions 
added  of  sulphuretted  hydrogen,  distinguishing  the  perox- 
ide of  mercury  from  all  other  substances.  It  is  caused 
by  the  formation,  at  first,  of  a  white-coloured  double  com- 
pound of  bisulphuret  of  mercury,  with  still  undecompos- 
ed  salt  of  peroxide  of  mercury,  which  then,  becoming 
more  and  more  mixed  with  black  bisulphuret,  causes  the 
precipitate  successively  to  assume  the  various  tints  de- 
scribed above.  Bisulphuret  of  mercury  is  not  dissolved 
by  hydrosulphuret  of  ammonia,  nor  by  cyanide  of  potas- 
sium ;  it  is  quite  insoluble  in  hydrochloric  acid  and  nitric 
acid,  even  on  being  boiled  with  these  acids.  Potash 
ley  dissolves  it  completely,  and  aqua  regia  decomposes 
and  dissolves  it  with  facility. 

3.  Potash,  when  added  in  insufficient  quantity  to  neutral 
or  feebly  acid  solutions  of  peroxide  of  mercury,  yields  with 
them  a  RED-BROWN  precipitate,  which  acquires  a  TELLOW 
tint  when  the  reagent  is  added  in  excess.  The  red-brown 
precipitate  is  a  BASIC  SALT  ;  the  yellow,  on  the  contrary, 
consists  of  pure  HYDRATED  PEROXIDE  OF  MERCURY.  (Hg. 


112  OXIDE   OF    COPPER. 

O,  HO.)  An  excess  of  the  precipitant  does  not  re-dis- 
solve these  precipitates.  In  very  acid  solutions  this  reac- 
tion either  does  not  take  place  at  all,  or  is  at  least  incom- 
plete. If  salts  of  ammonia  be  present,  the  precipitates 
formed  are  neither  red,  brown,  nor  yellow,  but  white  ; 
consisting  of  basic  compounds  of  peroxide  of  mercury  and 
ammonia. 

4.  Ammonia  causes  the  same  WHITE    PRECIPITATE, 
which  potash  produces  when   salts  of  ammonia  are  pre- 
sent. 

5.  Protochloride   of  tin,  when  added  in  small  propor- 
tions to  salts  of  peroxide  of  mercury,    causes  a  reduc- 
tiori  of  this  peroxide  to  protoxide,  in  consequence  of  which 
a  white  precipitate  of  PROTOCHLORIDE  OF  MERCURY  forms  ; 
but  when  added  in  excess,  it  completely  withdraws  the 
oxygen  and  acid  or  the  salt-radical  from  the  mercury  and 
causes  the  latter  to  separate  in  a  metallic  form,  just  as  is 
the    case    with  protoxide  of  mercury,   (vide   §  90,  b  6.) 
The  pfecipitate,  therefore,  which  in  the  first  place  was 
white,  acquires  now  a  gray  tint,  and  may  be  united  into 
globules  of  metallic  mercury,  by  being  boiled  with  hydro- 
chloric acid. 

5.  The  salts  of  peroxide  of  mercury  present  the  same 
relation  to  metallic  copper  as  those  of  the  protoxide  ; 
and  the  same  is  the  case  with  regard  to  their  behaviour 
before  the  blow-pipe,  when  mixed  with  carbonate  of  soda. 

b.    OXIDE    OF    COPPER.       (Cu  O.) 

1.  The  salts  of  oxide  of  copper  undergo  decomposition, 
even  at   a  gentle   red  heat,  with  the   exception  of  blue 
vitriol,  which  can  bear  a  somewhat  higher  temperature. 
They  present  in  their  anhydrous   state    a  white,  but  as 
hydrates,  a  blue  or   green  colour,  which  their  solutions 
still  retain,    though  rather  highly  diluted.     Most  of  the 
neutral  salts  of  oxide  of  copper  are  soluble  in  water  ;  those 
which  are  soluble  redden  litmus  paper. 

2.  Sulphuretted  hydrogen  and  liydrosulphuret  of  am- 
monia produce,  under  any  circumstances,    brown-black 
precipitates    of  BISULPHTJRET  OF  COPPER  (Cu   S.)     This 
substance  is  insoluble  in  dilute  acids  and  caustic  alkalies, 
as  well  as  in  hot  solutions  of  sulphuret  of  potassium  and 


OXIDE    OP  COPPER.  113 

of  sulphuret  of  sodium  ;  but  it  is  not  quite  insoluble  in 
hydrosulphuret  of  ammonia,  on  account  of  which  this 
reagent  is  not  applicable  for  the  separation  of  bisulphuret 
of  copper  from  other  metallic  sulphurets.  Boiling  concen- 
trated nitric  acid  readily  decomposes  and  dissolves  bi- 
sulphuret of  copper.  Solution  of  cyanide  of  potassium 
dissolves  it  completely. 

3.  Potash  produces  a  bright  blue,  bulky  precipitate  of 
HYDRATED  OXIDE  OF  COPPER,  (Cu  O,    HO.)     In   highly 
concentrated  solutions  this  precipitate  becomes,  on  addition 
of  potash  in  excess,  black,  and  loses  its  bulkiness,  even  at 
a  low  temperature,  after  some  time,  but  at  any  rate  on  being 
boiled  with  the  fluid   wherein  it  is  suspended.     In  this 
process  the  hydrated  oxide  is  converted  into  oxide. 

4.  Ammonia,  when  added  in  a  small  proportion,  produces 
a  GREENISH  BLUE  precipitate,  consisting  of  a  BASIC  SALT  OF 
COPPER.     This  precipitate  is  easily  redissolved  when  the 
addition  of  ammonia  is  continued  and  a  PERFECTLY  TRANS- 
PARENT MAGNIFICENTLY    AZURE   BLUE    SOLUTION   obtained, 

which  owes  its  colour  to  the  new-formed  BASIC  AMMONIACAL 
SALT  OF  OXIDE  OF  COPPER.  This  tint  vanishes  only  when 
the  solution  is  highly  diluted.  Potash  causes  in  this  blue 
solution — (at  a  low  temperature  only  after  having  been 
allowed  to  stand  at  rest  for  some  time) — a  precipitate  of 
BLUE  HYDRATED  OXIDE,  but  at  the  boiling  point,  it  precipi- 
tates the  entire  copper  as  BLACK  OXIDE.  Carbonate  of 
ammonia  presents  the  same  relation  to  salts  of  copper,  as 
pure  ammonia. 

5.  Ferrocyanide  of  potassium  produces  even  in  highly- 
dilute  solutions,  a  reddish-brown  precipitate  of  FERROCY- 
ANIDE OF  COPPER  (Cfy  +  2  Cu)  which  is  insoluble  in  dilute 
acids,  but  decomposed  by  potash. 

6.  Metallic  iron,  when  in   contact  with  concentrated 
solutions  of  copper,  is  almost  immediately  covered  with  a 

COPPERY    RED    CRUST    OF     METALLIC      COPPER  J    but     when 

the  copper  solution  is  highly  dilute,  this  coating  only  takes 
place  after  the  lapse  of  some  time.  This  test  is  very  deli- 
cate, but  especially  so,  when  the  solution  contains  a  free 
acid,  (e.  g.  hydrochloric  acid.) 

7.  If  copper  compounds,  mixed  with  carbonate  of  soda, 
be  exposed  on  a  charcoal  support  to  the  reducing  flame  of 


114  OXIDE    OF  BISMUTH. 

the  blow-pipe,  METALLIC  COPPER  is  obtained  without  simul- 
taneous incrustation  of  the  coal.  The  best  method  of 
examining  this  copper,  so  as  to  leave  no  doubt  of  its 
presence,  is  to  triturate  the  fused  mass  together  with  the 
surrounding  particles  of  the  charcoal  support,  in  a  mortar 
with  some  water,  and  then  to  wash  off  the  charcoal  powder. 
The  coppery-red  metallic  spangles  will  remain. 

C.    OXIDE    OF    BISMUTH.       (Bi  O.) 

1.  The  salts  of  bismuth  are  not  volatile,  with  the  excep- 
tion of  a  few,  (chloride  of  bismuth.)     Most   of  them  de- 
compose at  a  red  heat.     They  are  colourless  ;  some  are 
soluble  in  water,  whilst  others  are  insoluble.     The  soluble 
salts,  when  neutral  redden  litmus  paper,  and  are  d-ecompos- 
ed  by  much  water  into  soluble  acid  and  insoluble  basic  salts. 

2.  Sulphuretted    hydrogen    and    hydrosulphuret    of 
ammonia  produce,  under  all  circumstances,  black  precipi- 
tates of  SULPEIURET  OF  BISMUTH  (Bi  S)  which  are  insoluble 
in  dilute  acids,  alkalies,  alkaline  sulphurets,  and  cyanide  of 
potassium.     Boiling  concentrated  nitric   acid  readily   de- 
composes and  dissolves  it. 

3.  Potash  and   ammonia  throw  down  from  solutions  of 
salts  of  bismuth,  HYDRATED  OXIDE  OF  BISMUTH  (BiO,  HO) 
as  a  white  precipitate,  which  is, insoluble  in  an  excess  of 
he  precipitants. 

4.  Chromate  of  potash  precipitates  CHROMATE  OF  BIS- 
MUTH (Bi  O,  Cr  O3)  as  a  yellow  powder.     This  substance 
differs  from  chromate  of  lead,  inasmuch  as  it  is  soluble  in 
dilute  nitric  acid,  and  insoluble  in  potash. 

5.  The  reaction   which  particularly  characterizes   the 
oxide  of  bismuth,  is  the  decomposition  of  its  neutral  salts 
by  water  into  acid  soluble  and  basic  insoluble  salts.     For 
when  a  solution  of  bismuth  is  diluted  wTith  much  water,  a 
shining  white  precipitate  immediately  forms,  provided  free 
acid  be  not  present  in  a  too  large  proportion.     This  re- 
action is  the  most  susceptible  with  chloride  of  bismuth,  the 
basic  chloride  of  bismuth  being  almost  absolutely  insoluble 
in  water.     If  water  causes  no  precipitate  in  nitric  solu- 
tions  of.  bismuth,  owing  to  the  presence  of  a  too  large 
quantity  of  free  acid,  precipitation  may  immediately  be 
induced  by  the  addition  of  basic  acetate  of  lead  in  excess. 


OXIDE    OF    CADMIUM.  115 

Before  recurring  to  this  means,  we  must,  of  course,  be 
convinced  of  the  absence  of  sulphuric  acid,  &c.  &c.  The 
precipitates  of  bismuth  are  easily  to  be  distinguished  by 
means  of  their  insolubility  in  tartaric  acid,  from  the  basic 
salts  of  antimony  which  are  formed  under  analogous  cir- 
cumstances. 

6.  If  bismuth  compounds,  mixed  with  carbonate  of  soda, 
be  exposed  on  a  charcoal  support,  to  the  reducing  flame, 
BRITTLE  GRAINS  OF  BISMUTH  are  obtained,  which  fly  into 
pieces  under  the  stroke  of  the  hammer.  The  charcoal  at 
the  same  time  becomes  covered  with  a  slight  yellow  in- 
crustation of  OXID3  OF  BISMUTH- 

d.    OXIDE    OF    CADMIUM.       (Cd  0.) 

1.  The  salts  of  oxide  of  cadmium  are  either  colourless 
or  white  ;  most  of  them  are  soluble  in  water.     The  soluble 
salts,  when  neutral,  redden  litmus  paper  and  decompose 
at  a  red  heat. 

2.  Sulphuretted  hydrogen  and  hydrosulphuret  of  am- 
monia produce,  under  all  circumstances,  precipitates  of  a 
rich  yellow  colour,  consisting  of  sulphuret  of-  cadmium 
(Cd,  S.)     This  substance  is  insoluble  in  dilute  acids,  in 
alkalies,   alkaline   sulphurets,   and  cyanide  of  potassium. 
Boiling  concentrated  nitric  acid  readily  decomposes  and 
dissolves  it. 

3.  Potash  produces  a  white  precipitate  of  HYDRATED 
OXIDE  OF  CADMIUM  (Cd  O,  HO)  which  is  insoluble  in  an 
excess  of  the  precipitant. 

4.  Ammonia  also  precipitates  white  HYDRATED  OXIDE  OF 
CADMIUM,  but  readily  redissolves  into  a  colourless   fluid, 
when  added  in  excess. 

5.  Carbonate  of  potash  and  carbonate  of  ammonia  pro- 
duce white  precipitates  of  CARBONATE  OF  CADMIUM  (Cd  O, 
CO2)  which  are  insoluble  in  an  excess  of  the  precipitants. 
The  presence  of  salts  of  ammonia  does  not  prevent  the 
formation  of  these  precipitates. 

6.  If  cadmium  compounds  mixed  with  carbonate  of 
soda  be  exposed  on  a  charcoal  support,  to  the  reducing 

jlame,  the  charcoal  becomes  covered  with  a  REDDISH  YEL- 
LOW incrustation  of  OXIDE  OF  CADMIUM,  owing  to  the  re- 


116  OXIDE    OP   CADMIUM. 

duced  metal  immediately  volatilizing,  and  then  becoming 
reoxidized  in  passing  through  the  oxidizing  flame. 

Recapitulation  and  remarks. — The  metallic  oxides  of 
the  second  section  of  the  fifth»group  may,  as  we  have 
stated,  be  completely  separated,  by  means  of  hydrochloric 
acid,  from  protoxide  of  mercury  and  oxide  of  silver,  but 
only  incompletely  from  oxide  of  lead.  The  peroxide  of 
Tnercury  is  distinguished  from  the  other  oxides  of  this 
section,  by  the  insolubility  of  its  bisulphuret  in  boiling 
nitric  acid.  This  property  affords  a  convenient  means  for 
its  separation.  Moreover,  the  reactions  with  protoxide  of 
tin,  or  with  metallic  copper,  as  well  as  those  in  the  dry 
way,  readily  admit  of  its  detection  when  the  protoxide  has 
been  previously  removed. 

Of  the  still  remaining  oxides,  those  of  copper  and  cad- 
mium are  distinguished,  inasmuch  as  the  precipitates 
which  ammonia  causes  in  their  solutions,  are  soluble  in  an 
excess  .of  ammonia,  whilst  the  precipitates  which  this  re- 
agent produces  in  solutions  of  lead  and  bismuth,  are  not 
redissolved  by  an  excess  of  the  precipitant.  The  oxide  of 
bismuth  may  be  separated  from  the  oxide  of  lead  by  means 
of  sulphuric  acid,  but  is  most  safely  detected  by  the  de- 
composibility  of  its  salts  by  water.  The  other  tests  of 
lead  have  already  been  stated  in  the  first  section  of  this 
group.  The  oxide  of  copper  may  be  separated  from  the 
oxide  of  cadmium,  by  means  of  carbonate  of  ammonia ; 
the  former  is  especially  characterized  by  the  reactions  with 
ferrocyanide  of  potassium  and  with  iron,  as  well  as  by  its 
relations  before  the  blow-pipe  ;  and  oxide  of  cadmium  may 
always  be  detected  by  its  yellow  sulphuret,  which  is  in- 
soluble in  hydrosulphuret  of  ammonia,  and  by  the  charac- 
teristic incrustation  with  which  it  covers  charcoal  when 
exposed  to  the  reducing  flame.  For  a  separation  of  the 
oxides  of  the  fifth  group  from  each  other,  by  means  of 
cyanide  of  potassium,  we  refer  to  the  second  section  of 
Part  II. 


PEROXIDE    OF  GOLD.  1  17 

§  92. 
Sixth  Group. 

PEROXiDE  OF  GOLD,  PEROXIDE  OF  PLATINUM,  OXIDE  OF 
ANTIMONY,  PEROXIDE  OF  TIN,  PROTOXIDE  OF  TIN, 
ARSENIOU3  AND  ARSENIC  ACID.* 

Properties  of  the  group. — The  sulphurets  correspond- 
ing with  the  oxides  of  the  sixth  group  are  insoluble  in  dilute 
acids.  They  combine  with  alkaline  sulphurets,  forming 
soluble  sulphur  salts,  in  which  compounds  they  perform 
the  part  of  an  acid.  Sulphuretted  hydrogen,  therefore, 
precipitates  them  completely  from  acidified,  but  not  from 
alkaline  solutions.  The  precipitated  sulphurets  dissolve 
in  hydrosulphuret  of  ammonia,  sulphuret  of  potassium,  &c» 
&c.,  and  are  again  precipitated  from  these  solutions  by  the 
addition  of  acids. 

We  divicfe  the  oxides  of  this  group  into  two  classes,  and 
distinguish, 

1.  OXIDES  THE  CORRESPONDING  SULPHURETS  OP'WHICH 
ARE     INSOLUBLE    IN     HYDROCHLORIC    ACID    AND    IN    NITRIC 

ACID,  viz.  peroxide  of  gold  and  peroxide  of  platinum,  from 

2.  THOSE  THE  CORRESPONDING  SULPHURETS  OF  WHICH 
ARE  SOLUBLE    IN   HYDROCHLORIC   ACID    OR    NITRIC  ACID, 
viz-  oxide   of  antimony,    protoxide   and   peroxide  of  tin| 
arsenious  and  arsenic  acid. 

§  93. 

1  First  Class. 
Special  Reactions. 

a.    PEROXIDE    OF    GOLD.       (Au  03.) 

1.  Salts  of  gold  with  oxygen  acids  are,  at  present,  almost 
unknown.     The  haloid  salts  of  gold  are  yellow,  and  their 

*  The  two  acids  of  arsenic  will  be  again  referred  to,  when  we 
treat  of  the  relations  between  acids  and  reagents.  We  join  them 
here  to  the  metallic  oxides,  since  the  relation  of  sulphuret  of  arsenic 
easily  admits  of  their  being  confounded  with  several  oxides  of  the 
sixth  group,  and  because  in  analysis  we  always  obtain  the  sulphuret 
of  arsenic  as  a  precipitate,  together  with  sulphuret  of  antimony,  sul- 
phuret oftin,  &c.  &c. 
5* 


118  PEROXIDE    OF    PLATINUM. 

solutions  present  this  tint  up  to  a  high  degree  of  dilution. 
They  all  readily  decompose  at  a  red  heat ;  the  soluble  salts, 
when  neutral,  redden  litmus  paper. 

2.  Sulphuretted  hydrogen  precipitates  from  neutral  and 
acid  solutions  all  the  gold  they  contain,  as  black  SULPHURET 
OP  GOLD  (Au  S3)  which  is  insoluble  in  potash  and  in  any 
single  acid,  but  soluble  in  alkaline  sulphurets  and  in  aqua 
regia. 

3.  Hydrosulphuret  of  amm,onia  produces  the  same  pre- 
cipitate.   A  considerable"  excess  of  the  precipitant  redis- 
solves  it. 

4.  Potash  in  excess  causes  no  precipitation,  but  a  small 
proportion  of  potash  produces  in  concentrated   solutions, 
especially  when  heated,   a  reddish  yellow    precipitate  of 
PEROXIDE  OF  GOLD,  which  is  always  mixed  with  an  auric 
salt  of  cihloride  of  gold,  as  well  as  with  potash. 

5.  Ammonia  produces  also  only  in  concentrated  solu- 
tions, reddish  yellow  precipitates  of  AURATE  OF  AMMONIA 
(fulminating  gold.) 

6.  Protocldoride  of  tin,  containing  perchloride   of  tin, 
produces  even  in  highly  dilute  solutions  of  gold,  a  purple- 
red  precipitate  or  tint  at  least,  which  sometimes  inclines 
more  to  violet  or  to  brown-red.     This  precipitate  has  re- 
ceived the  name  of  PURPLE  OF  CASSIUS  ;  it  is  a  mixture 
of  peroxide  of  tin  and   metallic  gold,  and  is  insoluble  in 
hydrochloric  acid. 

7.  Protosalts  of  iron  reduce  the  peroxide  of  gold  when 
added  to  its  solutions,  and  precipitate  metallic  gold  as  a 
very  fine  brown  powder,  which  shows  a  metallic    lustre, 
when  pressed   upon  with  the  blade  of  a  knife,  or  when 
rubbed.     The  fluid  in  which  the  precipitate  is  suspended, 
appears  of  a  blackish-blue  colour,  by  transmitted  light. 

b.    PEROXIDE    OF    PLATINUM.       (Pt  Oz.) 

1 .  The  persalts  of  platinum  decompose  at  a  red  heat. 
They  are  of  a  red-brown  colour,  which  their  solutions  still 
show,  though  considerably  diluted.  The  soluble  salts  when 
neutral  redden  litmus  paper. 

2.  Sulphuretted  hydrogen  precipitates  from  acid  and 
neutral  solutions — (but  not  from  alkaline  solutions) — after 


OXIDE    OP   ANTIMONY.  119 

the  lapse  of  some  time  blackish-brown  SULPHURET  OP  PLA- 
TINUM (Pt  82.)  Potash  and  alkaline  sulphurets  dissolve 
It  when  added  greatly  in  excess.  Sulphuret  of  platinum 
is  insoluble  in  hydrochloric  acid  as  well  as  in  nitric  acid, 
but  dissolves  readily  in  aqua  regia. 

3.  Hydrosulphuret  of  ammonia  produces  the  same  pre- 
cipitate, which  completely  redissolves  in  a  large  excess  of 
the   precipitant.     Acids  precipitate  it  again  unaltered  from 
this  solution. 

4.  Potash  and  ammonia  produce  in  solutions  of  platinum 
when  not  too  highly  dilute,  yellow  crystalline  precipitates 

of  CHLORIDE  OF  PLATINUM  AND  POTASSIUM  and  of  CHLO- 
RIDE OF  PLATINUM  AND  AMMONIA,  which  are  insoluble  in 
acids,  but  soluble  in  an  excess  of  the  precipitants,  upon 
the  application  of  heat.  The  presence  of  free  hydrochloric 
acid  promotes  the  precipitation  in  a  high  degree,  by  effect- 
ing the  conversion  of  the  free  alkalies  into  chlorides. 

5.  Protochloride  of  tin  imparts  an  INTENSE  DARK  BROWN- 
ISH RED  COLOUR  to  solutions  of  persalts  of  platinum,  but 
without  yielding  a  precipitate ;  this  reaction  is  owing  to  a 
reduction  of  the  peroxide  or  the  perchloride  to  protoxide 
or  protochloride. 

Recapitulation  and  remarks. — The  reactions  of  gold 
and  platinum  afford,  at  least  partly,  the  means  of  detecting 
these  metals  as  well|when  many  other  oxides  are  present, 
as  also  and  especially,  when  platinum  and  gold  are  con- 
tained in  one  and  the  same  solution.  Protochloride  of  tin 
and  protoxide  of  iron  must  be  mentioned  here  as  particu- 
larly characteristic  tests  of  gold,  and  with  regard  to  pla- 
tinum the  same  may  be  said  of  potash  and  ammonia  with 
the  presence  of  free  hydrochloric  acid,  or  what,  in  fact,  is 
the  same,  of  chloride  of  potassium  and  muriate  of  am- 
monia. 

§  94. 

Second  Class  of  the  Sixth  Group. 
Special  Reactions. 

a.    OXIDE    OF    ANTIMONY.       (Sb  Os.) 

1 .  The  salts  of  oxide  of  antimony  partly  decompose  at 
a  red  heat ;  the  haloid  salts  volatilize  readily,  and  without 


120  OXIDE    OF    ANTIMONY. 

undergoing  decomposition.  The  soluble  neural  salts  of 
antimony  redden  litmus  paper.  The  solution  of  oxide  of 
antimony  in  hydrochloric  acid  is  characterized  by  the  na- 
ture of  the  decomposition  it  undergoes  when  diluted  with 
water  ;  in  this  decomposition,  an  acid  salt  remains  in  solu- 
tion whilst  a  basic  salt  is  thrown  down  as  a  white,  bulky 
precipitate,  which,  however,  after  some  time,  becomes 
dense  and  crystalline.  Tartaric  acid  readily  dissolves 
this  precipitate,  and,  consequently,  prevents  its  precipita- 
tion when  added  to  the  solution  before  the  dilution  with 
water.  It  is  by  this  property  that  the  basic  protochloride 
of  antimony  is  distinguished  from  the  basic  salts  of  bis- 
muth formed  under  analogous  circumstances.  The  oxide 
of  antimony,  in  whatever  manner  it  may  have  been  pre- 
pared, is  completely  soluble  in  a  hot  solution  of  bitartrate 
of  potash.- 

2.  Sulphuretted  Hydrogen  precipitates  the  oxide  of  an- 
timony from  neutral  solutions  very  incompletely,  from  al- 
kaline solutions  not  at  all,  but  from  acid  solutions  com- 
pletely, as  orange-red  SULPHURET  OF  ANTIMONY  (Sb  S3.) 
This  precipitate  is  readily  dissolved  by  potash  and  by  al- 
kaline sulphurets,  especially  if  the  latter  contain  sulphur 
in  excess,  whilst  it  is  almost  insoluble  in  ammonia,  and 
totally  so  in  bicarbonate  of  ammonia,  when  free  from  any 
admixture  of  sulphur,  as  well  as  from  sulphantimonious  and 
sulphantimonic  acid.  It  is  insoluble  in  dilute  acids.  Con- 
centrated boiling  hydrochloric  acid  dissolves  it,  with  evo- 
lution of  sulphuretted  hydrogen  gas.  When  heated,  with 
free  access  of  air,  it  is  converted  into  a  mixture  of  anti- 
monious  acid  with  sulphuret  of  antimony.  When  defla- 
grated with  saltpetre,  it  yields  sulphate  of  potash  and  an- 
timoniate  of  potash.  If  a  potash  solution  of  sulphuret  of 
antimony  be  boiled  together  with  oxide  of  copper,  sul- 
phuret of  copper  is  formed,  and  oxide  of  antimony  dis- 
solved in  potash  remains  in  solution. 

3.  Hydrosulphuret*  of  ammonia  produces  an  orange- 
red  precipitate  of  SULPHURET  OF  ANTIMONY,  which  readily 
redissolves  in  an  excess  of  the  precipitant.  Acids  pre- 
cipitate from  this  solution  the  sulphuret  of  antimony  unal- 
tered. But  the  colour  of  this  second  precipitate  usually 
appears  somewhat  lighter,  owing  to  an  admixture  of  sul- 
phuf. "  ',  ' 


OXIDE    OF  ANTIMONY.  121 

4.  Potash,  ammonia^  carbonate  of  potash,  and  carbonate 
of  ammonia,  throw  down  from  the   solutions  of  simple 
salts  of  oxide  of  antimony, — but  not,  at  least  not  immedi- 
ately, from  those  of  tartar  emetic  or  analogous  compounds, 
— a  white  and   bulky  precipitate  of  HYDRATED  OXIDE  OF 
ANTIMONY  Sb  O3,  HO)  which  readily  redissolves  in  an 
excess  of  potash,  but  is  very  difficult  of  solution  in  an  ex- 
cess of  the  other  three  precipitants. 

5.  Metallic  zinc  precipitates  from  all  solutions  of  oxide 
of  antimony,  unless  containing  free  nitric  acid,  METALLIC 
ANTIMONY  as  a  BLACK  POWDER.     But  if  they  contain  free 
nitric  acid,  a  precipitate  of  oxide  of  antimony  forms  simul- 
taneuiisly  with  the  metallic  precipitate. 

6.  If  a  solution  of  oxide  of  antimony  is  mixed  with  zinc 
and  sulphuric  acid,  the  zinc  oxidizes  not  only  at  the  ex- 
pense of  the  oxygen  of  the  water,  but  also  at  the   expens  e 
of  that  of  the  oxide  of  antimony.     Antimony,   therefore, 
separates  in  its  METALLIC  STATE,  but  a  portion  of  the 
metal  in  the  moment  of  its  separation  combines  with  the 
liberated  hydrogen  of  the  water,  forming  ANTIMONIURETTED 
HYDROGEN  (Sb  H.{.)     Ifthis   operation  be   conducted  in  a 
gas-evolution  flask,  connected  by  means  of  a  perforated  cork 
with  one  limb  of  a  bent  tube,  the  other  limb  of  which  ends 
in    a  finely  drawn-out  point,  pinched  off  at  the  top,*)  and 
the  hydrogen  passing  through  this  fine  aperture,  be  kindled, 
after  all  atmospheric  air  has  been  previously  expelled,  the 
flame  appears  of  a  bluish-green,  owing  to   the  antimony 
separating  in  a  state  of  intense  heat,  during  the  combustion 
of  the  antimoniuretted  hydrogen  ;  white  fumes  of  oxide  of 
antimony  rise  from  the  flame,  which  readily  condense  upon 
cold  substances,  and  are  not  dissolved  by  water.     If  a  cold 
substance  (such  as  a  porcelain  plate)  be  depressed  upon  the 
flame,  a  deep  black  and  almost  lustreless  spot  of  metallic 
antimony  in  a  state  of  minute  division  is  formed  upon  the 
surface  of  the  plate.     If  the  tube  through  which  the  gas  is 
passing  be  heated  to  redness  in   the  middle,  the  bluish- 

*  In  very  minute  and  exact  experiments,  it  is  necessary  further  to 
transmit  the  gas  through  another  connecting  tube,  loosely  filled  with 
cotton,  in  order  to  prevent  it  from  carrying  with  it  any  moisture  with 
which  it  may  be  charged,  into  the  emission  part  of  the  tube.  Vide 
engraving  of  Marsh's  apparatus  for  the  reduction  of  arsenic,  §  94  d  7. 


122  PROTOXIDE    OF    TIN. 

green  tint  of  the  flame  disappears,  and  a  metallic  mirror 
of  antimony  of  silvery  lustre  is  formed  within  the  tube  on 
both  sides  of  the  heated  spot.  If  a  stream  of  dry  sulphu- 
retted hydrogen  be  now  very  slowly  transmitted  through 
this  tube,  and  the  mirror  be  heated  by  a  spirit-lamp,  from 
its  outer  towards  its  inner  extremity,  i.  e.  in  a  direction 
opposite  to  that  of  the  gas  stream,  the  mirror  of  antimony 
changes  into  sulphuret  of  antimony,  which  appears  of  a 
more  or  less  red-yellow  colour,  and  almost  black  when  in 
thick  layers.  If  a  weak  stream  of  dry  hydrochloric  acid 
gas  be  then  transmitted  through  the  same  glass  tube,  the 
sulphuret  of  antimony  disappears,  immediately,  when  only 
present  in  thin  layers,  and,  after  a  few  seconds,  when  the 
incrustation  is  somewhat  thicker.  For  sulphuret  of  anti- 
mony readily  decomposes  with  hydrochloric  acid  gas,  and 
the  nascent  chloride  of  antimony  is  very  volatile  in  the 
stream  of  hydrochloric  acid  gas.  If  this  gas  stream  be 
transmitted  through  water,  the  presence  of  antimony  in  the 
latter  may  easily  be  proved  by  means  of  sulphuretted  hy- 
drogen. By  this  combination  of  reactions,  antimony  may 
be  distinguished  with  certainty  from  all  other  metals. 

7.  If  compounds  of  antimony  mixed  with  carbonate  of 
soda,  on  a  charcoal  support,  be  exposed  to  the  reducing 
blow-pipe  flame,  BRITTLE  GLOBULES  OF  METALLIC  ANTI- 
MONY are  obtained.  At  the  same  time,  volatilization  of 
the  reduced  and  reoxidized  metal  takes  place,  which,  even 
after  the  removal  of  the  test  specimen  from  the  flame,  con- 
tinues for  some  time,  and  becomes  especially  evident  when 
a  stream  of  air  is  directed  by  means  of  the  blow-pipe 
upon  the  surface  of  the  cooling  mass.  The  oxide  formed 
is  partly  deposed  on  the  charcoal  as  a  white  crust,  and 
partly  surrounds  the  metallic  globule  in  the  form  of  fine 
crystalline  needles. 

b.     PROTOXIDE    OF    TIN.       (Sn  O.) 

1.  The  protosalts  of  tin  are  colourless,  and  decompose 
when  heated.  The  soluble  salts  when  neutral,  redden 
litmus  paper.  When  solutions  of  neutral  stannous  salts 
are  diluted  with  water,  they  become  turbid  and  of  a  milky- 
white  colour,  owing  to  their  decomposition  into  soluble 
acid  and  insoluble  basic  salts.  The  addition  of  hydro- 
chloric acid  causes  the  milkiness  to  disappear. 


PROTOXIDE    OF    TIN.  123 

2.  Sulphuretted  hydrogen  precipitates  from  neutral  and 
acid,  but  not  from  alkaline   solutions,   dark  brown  SUL- 
PHURET  OF  TIN,  (Sn  S,)  which  is  soluble  as  well  in  potash 
and  in   alkaline  sulphurets,  especially  in  such  as  contain 
larger  proportions  of  sulphur,  as  also  in  concentrated  boil- 
ing hydrochloric  acid.     Boiling  nitric  acid  converts  it  into 
insoluble  peroxide  of  tin.  - 

3.  Hydrosulphuret  of  ammonia  occasions  the  same  pre- 
cipitate  of  SULPHURET  OF  TIN,  which  very  sparingly  dis- 
solves in  an  excess  of  the  precipitant.     If  the  hydrosul- 
phuret  of  ammonia  has  already  turned  yellow,   i.  e,  if  it 
contains  an  excess  of  sulphur,  or  if  finely  powdered  sulphur 
be  added,  the    solution  is  much   facilitated.     From  this 
solution,  in  hydrosulphuret  of  ammonia,  with  excess  of 
sulphur,  acids  precipitate  yellow  bisulphuret  of  tin  mixed 
with  sulphur. 

4.  Potash,  ammonia,  carbonate  of  potash,  and  carbonate 
of  ammonia,  produce    a  white   and  bulky  precipitate  of 
HYDRATED  PROTOXIDE  OF  TIN,  (Sn  O,  HO,)  which  readily 
dissolves  in  an  excess  of  potash,   but  is  insoluble  in  an 
excess  of  the  other  three  precipitants. 

5.  Per  chloride  of  gold  produces  in  solutions  of  pro- 
tochloride  or   protoxide  of  tin,  a  precipitate  or  tinge  of 
PURPLE  OF  CASSIUS,  on  the  addition  of  some  nitric  acid, 
(without  the  application  of  heat,)  vide  §  93,  a.  6. 

6.  If  to  a  solution  of  protochloride  or  protoxide  of  tin, 
solution  of  perchloride  of  mercury  be  added  in  excess,  a 
white  precipitate  of  PROTOCHLORIDE  OF  MERCURY  will  be 
formed  owing  to  the  salt  of  tin  depriving  the  perchloride  of 
mercury  of  half  its  chlorine. 

7.  If  proto-compounds  of  tin  be  mixed  with  carbonate 
of  soda  and  some  borax,  or  better  still,  with  equal  parts  of 
carbonate  of  soda  and  cyanide  of  potassium,  and  then,  on 
a  charcoal  support,  be  exposed  to  the  inner  blow-pipe 

flame,  ductile  grains  of  METALLIC  TIN  will  be  obtained, 
without  simultaneous  incrustation.  They  may  be  most 
easily  detected  by  scraping  off  the  specimen  and  the  par- 
ti cles  surrounding,  that  part  of  the  charcoal  which  con- 
tained the  specimen,  strongly  triturating  them  in  a  mortar* 
and  washing  the  coal  off  from  the  metallic  particles. 


124  PEROXIDE  OF  TIN. 


C.  PEROXIDE  OF  TIN.   (Sn  02.) 

1.  Peroxide  of  tin  exists  in  two  modifications  which  ex- 
hibit a  different  relation  to  solvents.     When  precipitated 
from  its  salts,  by  alkalies,  it  is  easily  soluble  both  in  pot- 
ash and  acids,  but  when  produced  by  oxidation  of  metallic 
tin  by  means  of  nitric  acid,  it  is  insoluble  in  these  solvents, 
(the  precipitated  oxide  of  tin  also  becomes  insoluble  on 
being  heated  to  redness.)     The  insoluble  modification  is 
converted  into  the   soluble,  by  fusion  with  carbonate  of 
soda.  - 

2.  The  persalts  of  tin  are  colourless  and  decompose  at  a 
red  heat.  The  soluble  neutral  persalts  of  tin  redden  litmus 
paper. 

3.  Sulphuretted  hydrogen  throws  down,  from  acid  and 
neutral  solutions,  a  yellow  precipitate  of  BISULPHURET  OF 
TIN,   (Sn  82.)     Alkaline   solutions  are   not  precipitated. 
The  bisulphuret  of  tin  is  soluble  in  pure  alkalies,  in  alka- 
line carbonates  and    bicarbonates,  in  alkaline  sulphurets, 
and  in  concentrated  and  boiling  hydrochloric  acid.     Nitric 
acid  converts  it  into  insoluble  peroxide  of  tin.     On  defla- 
grating bisulphuret  of  tin  with  nitre,  sulphate  of  potash,  and 
stannate  of  potash  are  formed.  If  a  solution  of  bisulphuret 
of  tin  in  potash  be  boiled  with  oxide  of  copper,  sulphuret 
of  copper  and  peroxide  of  tin  will  be  formed,  which  latter 
substance  remains  in  solution  in  the  potash. 

4.  Hydrosulphuret  of  ammonia  produces  the  same  pre- 
cipitate of  BISULPHURET  OF  TIN,  which  readily  redissolves  in 
an  excess  of  the  precipitant.  Acids  reprecipitate  from  their 
solution,  the  bisulphuret  of  tin  in  its  unaltered  state. 

5.  Potash  and  ammonia,  carbonate  of  potash  and  car- 
bonate of  ammonia,   precipitate   a  white    HYDRATED  PE- 
ROXIDE OF  TIN,  which  readily  redissolves  in  potash  and  car- 
bonate of  potash    (in    excess,)  but  is  sparingly  soluble  in 
ammonia,  and  quite  insoluble  in  carbonate  of  ammonia. 

6.  Metallic  zinc  precipitates,  from  solutions  of  perchlo- 
ride  or  persalts  of  tin,  when  containing  no  free  nitric  acid,  ME- 
TALLIC TIN,  in  the  shapeof  small  gray  leaves  or  as  a  spongy 
mass.     If,  on  the  contrary,  nitric  acid    be  present,  white 
peroxide  or  a  mixture  of  metallic  tin  and  of  peroxide  of  tin 
will  precipitate. 


ARSENIOUS   ACID.  125 

7.  The  per-compounds  of  tin  exhibit  the  same  proper- 
ties before  the  blow-pipe  as  the  proto-compounds. 

d.  ARSENIOUS    ACID.       (AsOs.) 

1 .  Arsenious  acid  on  being  heated  volatilizes  in  white 
inodorous  vapours.     Its  salts,  on  being  heated  to  redness, 
generally  are  decomposed  into  fixed  arseniates  and  arsenic, 
which  volatilizes.     Of  the  arsenites,  only  those  with  an 
alkaline  base  are  soluble. 

2.  Sulphuretted  hydrogen  precipitates  the  solutions  of 
arsenious  acid  and  of  neutral  arsenites,  slowly  and  incom- 
pletely, but  when  a  free  acid  is  present,  totally  and  imme- 
diately ;  these   precipitates  have  a  lively  yellow  colour. 
Alkaline  solutions  are  not  precipitated.     The  yellow  pre- 
cipitate of  SULPHO-ARSENIOUS  ACID,  (As  S3,)  is  readily 
and   completely  redissolved   in  pure   alkalies,  in  alkaline 
carbonates  and   bicarbonates,  and  in   alkaline  sulphurets, 
but  is  almost  insoluble  in  hydrochloric  acid.  Boiling  nitric 
acid  readily  decomposes  and  dissolves  it.     On  deflagrating 
it  with  carbonate  of  soda  and  nitrate  of  potash,  arseniated 
alkali  and  sulphated  alkali  are  obtained.     When  a  solution 
of  sulpharsenious  acid  in  potash  is  boiled   with  oxide   of 
copper,  sulphuret  of  copper  and  arseniate  of  potash  are 
formed ;  and  when  the  same  solution  is  boiled  with  pure 
oxide  of  bismuth,  or  with  a  carbonate  of  basic'  nitrate  of 
the  same  substance,   sulphuret  of  bismuth  and  arsenious 
acid  are  formed.     If  sulpharsenious  acid  be  mixed  with 
from  three  to  four  parts  of  carbonate  of  soda,  with  the  ad- 
dition of  some  water,  and  the  magma  be  then  spread  over 
some  small  glass  splinters,  and  the  latter,  after  having  been 
well  dried,  be  rapidly  heated  to  redness,  in  a  glass   tube, 
(c.  vide  sketch,)  through  which  dry  hydrogen  gas  is  trans- 
mitted, half  of  the  arsenic  contained  in  the  mixture  forms 
a  metallic  mirror  within  the  tube.     For  when  fusing  two 
eq.  of  sulpharsenious  acid,  together  with  four  eq.  of  soda 
sulpharsenico  sulphuret  of  sodium  and  arsenite  of  soda  are 
formed  ;   heating  these  products  in  hydrogen  gas,  all  the 
arsenic  is  expelled,  if  the  heat  is   strong  and   continuous. 
This  method,  although  a   great    portion  of  the  reduced 
arsenic  is  carried  off,    suspended    in    the  hydrogen  gas, 
yields,   nevertheless,  very  good  results.    If  the  hydrogen 


126  ARSENIOUS    ACID 

gas  be  kindled  at  the  exit  aperture  of  the  tube  c,  and  a 
cold  porcelain  plate  depressed  on  the  flame,  this  arsenic 
(carried  away  with  the  hydrogen  gas)  will  condense  upon 
the  plate.  If  a  red  heat  be  applied  to  another  part  of  the 
tube  Cj  more  towards  its  anterior  aperture,  (the  part  first 
heated  being  at  the  same  time  maintained  at  a  red  heat,) 
another  sublimate  will  be  formed  beyond  the  heated  spot, 
the  particles  of  arsenic  carried  away  with  the  stream  of  the 
hydrogen  gas,  being  reconverted,  at  the  red  hot  spot,  into  ar- 
senic vapours  in  a  state  of  expansion,  and  thus  condensing 
again  as  a  sublimate,  on  coming  into  contact  with  the  cold  part 
of  the  glass  tube.  If  the  heat  thus  simultaneously  applied 
to  two  parts  of  the  tube  be  strong,  whilst  the  stream  of 
the  hydrogen  gas  is  feeble,  scarcely  any  arsenic  will  be 
carried  away  with  the  gas.  No  arseniuretted  hydrogen  is 
formed  in  this  operation  and  those  who  explain  the  pheno- 
mena just  described,  by  the  formation  of  arseniuretted  hy- 
drogen, are  in  error.  (Fresenius  and  Babo.)  The  appa- 
ratus may  be  constructed  as  in  the  annexed  sketch. 


a  is  the  evolution  flask,  b  a  tube  containing  chloride  of  cal- 
cium, c  the  tube  in  which,  at  the  point  d,  the  glass  splin- 
ter with  the  specimen  is  placed.  This  part  is  then  (the 
apparatus  being  completely  filled  with  pure  hydrogen  gas) 
exposed  to  a  slight  heat,  at  first,  in  order  to  expel  all 
moisture,  and  then  suddenly  to  a  very  strong  heat,  (this  is 
best  done  with  a  blow-pipe,)  to  prevent  the  sublimation 
of  undecomposed  sulphuret  of  arsenic.  The  metallic  mfrror 
is  formed  near  the  point  e. 


ARSENIOUS    ACID.  127 

3.  Hydrosulphuret  of  ammonia  causes  also  the  forma- 
tion of  SULPHARSENIOUS  ACID.     In  neutral  or  alkaline  so- 
lutions, however,  this  substance    is  not  precipitated,  but 
remains  in  solution  as  sulpharsenico  sulphuret  of  ammo- 
nia.    On  the  addition  of  free  acid  it  precipitates  imme- 
diately from  this  solution. 

4.  Nitrate  of  silver  produces  in  neutral  solutions  of  the 
arsenites,  a  yellow  precipitate  of  ARSENITE  OF  SILVER, 
(2  Ag  O,  As  O.)  which   is  soluble  both  in  dilute  nitric 
acid    and    in    ammonia.    AMMONIO-NJTRATE  OF    SILVER 
yields  the  same  precipitate  with  solutions  of  arsenious  acid 
or  arsenites  when  containing  free  acid. 

5.  Sulphate  of  copper  and  ammonio  sulphate  of  copper 
produce,  under  the  same  circumstances   as  the   salts  of 
silver,  yellow  £reen  precipitates  of  ARSENITE  OF  COPPER, 
(2  Cu  O,  As  O3.) 

6.  If  arsenious  acid  be  dissolved  in  solution  of  caustic 
potash  in  excess,  or  if  the  solution  of  an  alkaline  arsenite 
be  mixed  with  caustic  potash,  and  a  few  drops  of  a  dilute 
solution  of  sulphate  of  copper  be   added  and  the  mixture 
boiled,  a  red  precipitate  of  protoxide  of  copper  is  formed, 
and  arseniate  of  potash  remains  in  solution.     This  reac- 
tion is  highly  sensible,  provided  only  a  minute  quantity  of 
solution  of  blue  vitriol  be  used*     If  the  red  precipitate  of 
protoxide  of  copper  is  no  longer  distinctly  visible  on  the 
light  falling  through  the  tube  in  which  the  solution  is  con- 
tained, it  will  yet  be  distinctly  seen  on  looking  in  at  the 
top  of  the  tube.     That  this  reaction,  though   really  im- 
portant in  individual  cases  as  a  confirmatory  test  of  arse- 
nious  acid,  and  especially  as  a  means  of  distinguishing 
arsenious  acid  from  arsenic  acid,  yet  cannot  be  employed 
as  a  means  of  directly  detecting  the  presence  of  arsenic, 
is  a  matter  of  course,  since  grape  sugar  and  other  organic 
substances  in  the  same  manner  separate  protoxide  of  cop- 
per from  salts  of  copper. 

7.  If  an  acid  or  neutral  solution  of  arsenious  acid,  or  of 
an  arsenite,  be  mixed  with  zinc,  water,  and  sulphuric  acid, 
ARSENIURETTED  HYDROGEN  (As  Ha)  will  be  formed  ;  for 
the  mode  of  its  formation  we  refer  to  §  94,  a  6.     This  pro- 
perty of  arsenic  affords  us  a  most  delicate  test  for  its  de- 
tection, and  a  highly  important  means  for  its  isolation.  The 


128 


ARSENIOUS    ACID. 


operation  is,  under  all  circumstances,  conducted  in  the  ap- 
paratus alluded  to,  §  94,  a  6,  of  which  we  annex  a  sketch. 


a  is  the  evolution  flask,  containing  fragments  of  metal- 
lic zinc,  and  water;  6  a  funnel  tube,  through  which  the 
sulphuric  acid,  and  afterwards  the  liquor  to  be  tested  for 
arsenic,  are  poured  into  the  flask ;  c  is  a  glass  tube,  loosely 
filled  with  smooth  cotton,%to  which  a  bent  tube,  d,  is  fitted 
by  means  of  a  perforated  cork  ;  this  tube  is  drawn  out  into 
a  point,  at  its  emission  extremity,  e,  and  pinched  off  at  the 
top.  When'the  evolution  of  hydrogen  has  proceeded  for 
some  considerable  time,  so  that  it  may  safely  be  inferred 
that  all  atmospheric  air  has  been  expelled  from  the  appar- 
atus, the  gas  is  kindled  at  the  emission  aperture  of  the 
tube,  d,  e.  (It  is  advisable  to  envelop  the  flask  with  a 
piece  of  cloth  before  kindling  the  gas,  as  an  eifectua  means 
of  preventing  any  accident,  should  an  explosion  take  place. ) 
It  is  absolutely  necessary  to  ascertain,  first,  whether  the 
zinc  and  the  sulphuric  acid  are  quite  free  from  arsenic. 
For  this  purpose,  1st,  a  porcelain  plate  is  depressed  upon 
the  flame,  and,.  2d,  the  tube  d  e  is  heated  to  redness  in  the 
middle,  the  limb  e  being  turned  into  a  horizontal  position 
for  this  purpose.  If  no  incrustation  be  formed,  neither  on 
the  plate  nor  in  the  tube,  the  zinc  and  sulphuric  acid  con- 
tain no  arsenic.  The  liquor  to  be  tested  is  then  introduced 
into  the  flask  through  the  funnel  tube.  If  it  contain  arsenic, 


ARSENIOUS    ACID.  129 

arseinuretted  hydrogen  will  be  evolved  together  with  the 
hydrogen,  imparting  a  bluish  tint  to  the  flame,  owing  to  the 
arsenic  separating  at  a  red  heat.  At  the  same  time  white 
fumes  of  arsenious  acid  are  observed,  which  condense  upon 
cold  objects.  If  a  porcelain  plate  be  now  depressed  upon 
the  flame,  black  spots  are  formed  on  its  surface,  owing  to 
the  reduced  and  not  yet  reoxidized  arsenic  condensing  on 
the  plate.  (Tide  antimony,  §  94,  a  6.)  Arsenic  spots  are 
of  a  rather  blackish  brown  colour,  and  bright  metallic  lus- 
tre ;  whilst  those  of  antimony  are  of  a  deep  black  colour, 
and  but  very  feebly  lustrous.  If  the  tube  d  e  be  heated  to 
redness  in  the  middle  of  its  limb  d,  the  arsenic  will  con- 
dense in  the  cold  part  of  the  tube,  forming. a  particularly 
beautiful  and  distinct  metallic  crust,  which  is  of  a  darker 
appearance  and  less  silvery  than  that  formed  by  antimony 
under  similar  circumstances  ;  it  may,  moreover,  be  clearly 
detected  by  the  characteristic  odour  of  garlic  which  is  per- 
ceived, if  the  tube  is  cut  off  near  the  incrustation,  and  the 
latter  then  volatilized  by  heat.  The  characteristic  odour 
of  alcarsin  (vide  10  seq.)  is  even  a  safer  indication  than 
that  of  garlic.  If  the  metallic  spots  of  crust  formed  on  the 
porcelain  plate  seem  to  indicate  the  presence  of  arsenic,  it 
is  still  necessary  to  make  quite  sure  that  it  is  really  a^nic 
and  not  antimony  we  have  before  us,  for  even  the  charac- 
teristic odour  of  garlic  or  alcarsin  is  not  sufficient  to  set 
all  doubts  at  rest  as  to  this  point.  The  following  are  the 
best  methods  of  ascertaining  the  presence  of  arsenic  be- 
yond doubt : — 

#,  fine  and  distinct  metallic  mirror  is  formed  within  the 
tube  through  which  the  arseniuretted  hydrog^i  passes,  on 
heating  its  middle  part  to  redness.  A  very  feeble  stream 
of  dry  sulphuretted  hydrogen  is  then  transmitted  through 
this  tube,  with  simultaneous  application  of  the  heat  of  a 
spirit-lamp  to  the  metallic  crust,  from  its  outer  towards  its 
inner  extremity.  If-arsenic  alone  be  present,  a  yellow  sul- 
plmret  of  arsenic  will  be  formed  within  the  tube  ;  and  if 
antimony  alone  be  present,  an  orange  or  black  sulphuret  of 
antimony  :  but  if  both  metals  be  present,  both  sulphurets 
will  be  formed  side  by  side,  the  sulphuret  of  arsenic,  as  the 
more  volatile,  always  preceding  the  sulphuret  of  anti- 
mony. Not  long  ago,  this  conversion  of  antimony  and 


130  ARSENIOUS   ACID. 

arsenic  into  sulphurets  was  suggested  as  the  surest  means 
of  distinguishing  these  two  metals  from  each  other.  Ex- 
perience has,  however,  taught  us  that  these  differences  in 
colour  and  volatility  are  not  striking  enough  to  prevent  the 
possibility  of  mistakes.  But  if  dry  hydrochloric  acid  gas 
be  transmitted  through  the  tube  containing  the  deposit 
under  examination,  without  application  of  heat,  no  altera- 
tion whatever  will  take  place  if  sulphuret  of  arsenic  alone  is 
present,  even  if  the  gas  be  transmitted  through  the  tube 
for  a  considerable  time.  If  sulphuret  of  antimony  alone  be 
present,  it  will  entirely  vanish,  and  if  both  sulphurets  be 
present,  the  sulphuret  of  antimony  will  vanish  immediately, 
whilst  the  yellow  sulphuret  of  arsenic  remains.  If  a  small 
quantity  of  ammonia  be  then  introduced  into  the  tube,  the 
sulphuret  of  arsenic  will  dissolve,  and  may  thus  easily  be 
distinguished  from  the  sulphur,  which,  peradventure,  may 
have  separated.  My  personal  experience  has  convinced 
me  of  the  infallibility  of  these  tests  for  the  detection  of 
arsenic. 

b.  The  limb  e  (vide  sketch  of  the  apparatus)  is  turned 
into  an  horizontal  position,  and  the  gas  kindled  and  made 
to  burn  in  a  small  glass  receiver,  having  a  capacity  of  about 
twe^e  ounces.  This  receiver  is  placed  in  a  beaker  glass 
filled  with  cold  water,  and  constantly  turned  and  moved, 
so  as  to  prevent  its  becoming  hot.  After  some  time, 
when  the  oxygen  in  the  receiver  becomes  exhausted,  and 
the  flame  grows  feeble,  another  is  substituted  for  the  first, 
and  several  are  filled  in  this  manner.  They  contain,  1st, 
arsenious  acid  alone,  or,  2d,  oxide  of  antimony  alone,  or, 
3d,  both  together.  If  the  first  be  the  case,  the  white  sub- 
limate obtained  will  completely  dissolve  in  hot  water,  ami 
the  solution  may  then  be  further  tested  for  arsenic.  In  the 
second  case,  nothing  will  dissolve,  nor  in  the  third,  if  the 
oxide  of  antimony  is  present  in  sufficient  quantity,  as  this 
gives  rise  to  the  formation  of  arsenite  of  antimony.  The 
arsenic  in  this  last  case  may  be  detected  by  dissolving  the 
sublimate  in  slightly  dilute  solution  of  potash,  and  adding 
sulphuretted  hydrogen  first,  and  then  bicarbonate  of  am- 
monia in  excess*  All  the  antimony  will  precipitate  as. 
sulphuret  of  antimony,  whilst  the  sulphuret  of  arsenic 
remains  dissolved  in  the  excess  of  bicarbonate  of  ammonia. 


ARSENIOUS    ACID.  131 

The  sulphuret  of  arsenic  precipitates  on  the  addition  of 
hydrochloric  acid  to  the  solution,  till  an  acid  reaction 
becomes  manifest.  Marsh  was  the  first  who  suggested 
the  method  of  detecting  arsenic  by  the  production  of  arse- 
niuretted  hydrogen. 

8.  If  arsenious  acid  or  an  arsenite  be  mixed  with  car- 
bonate of  soda  and  charcoal,  and  the  mixture  (which 
must  be  perfectly  dry)  be  then  heated  over  a  spirit-lamp 
to  redness,  in  a  well-dried  glass  tube,  closed  at  one  end, 
and  drawn  out  into  a  point  at  the  other,  the  charcoal  will 
oxidize  at  the  expense  of  the  oxygen  of  the  arsenious  acid, 
and  arsenic  will  become  liberated,  which  volatilizes  and 
condenses  above  the  heated  part  of  the  tube,  forming  a 
more  or  less  dark  brown  metallic  mirror  of  great  lustre. 
This  crust  may  be  further  driven  on  in  the  tube  by  gra- 
dually heating  the  latter  to  redness  towards  its  emission 
aperture,  and  may  thus  finally  be  expelled,  when  the  cha- 
racteristic odour  of  arsenic  (on  volatilizing  in  the  air)  will 
afford  a  further  proof  of  its  presence.  For  the  reduction 
of  the  free  arsenious  acid,  a  mere  fragment  of  charcoal  is 
used,  instead  of  carbonate  of  soda  and  charcoal ;  the  arse- 
nious acid  is  introduced  into  the  drawn-out  point  of  the 
tube,  the  fragment  of  charcoal  is  placed  over  it  and  heated 
to  redness  ;  heat  is  then  applied  to  the  point  of  the  tube. 
This  process  has  the  advantage  over  the  former  of  not 
soiling  the  tube,  which  is  done  when  operating  with  car- 
bonate of  soda  and  charcoal.  The  non-appearance  of  the 
metallic  crust  is  not  always  a  sure  sign  that  no  arsenic  is 
present,  when  testing  a  supposed  arsenite  by  means  of 
carbonate  of  soda  and  charcoal,  as  there  are  several  com- 
pounds of  arsenious  acid,  especially  of  those  with  heavy 
metallic  oxides,  as  e.  g.  oxide  of  iron,  which  do  not  yield 
metallic  mirrors. 

9.  If  arsenites,  or  arsenious  acid,  or  a  sulphuret  of  arse- 
nic, be  fused  together  with  a  mixture  of  dry  carbonate  of  1 
soda  and  cyanide  of  potassium,  all  the  arsenic  contained 
in  the  test  specimen  will  become  reduced,  under  all  cir- 
cumstances, and  sometimes  the  bases  also,  if  their  proper- 
ties admit  of  this  reduction ;  in  this  process  the  oxygen 
which  these  substances  lose,  converts  a  portion  of  the 
cyanide  of  potassium  into  cyanate  of  potash.  The  opera- 


132  ARSENIOUS    ACID. 

tion  is  conducted  in  the  following  manner : — the  arsenic 
compound,  which  must  be  perfectly  dry,   is  put  into  a 
small  glass  tube,   expanded  into  a  bulb  at  one  end,  and 
covered  with  six  fimes  its  quantity  of  the  mixture  of  per- 
fectly dry  carbonate  of  soda  and  cyanide  of  potassium. 
The  quantity  of  the  whole  mass  must  not  fill  more  than 
half  of  the  bulb,  or  else  the   cyanide  of  potassium,  when 
in  fusion,  will   get  into  the  tube.     The  heat  of  a  spirit- 
lamp   is    then  applied  to  the  bulb,  and  continued,  as  the 
arsenic  often  requires  some  time  for  its  complete  sublima- 
tion.    The  mirrors  which  are  obtained  in  this  process  are 
of  exceeding  purity.     These  crusts  are  produced  from  all 
arsenites,  the  bases  of  which  remain  either  altogether  un- 
reduced, or  are  converted  into  such   arseniurets  as  partly 
£>r  totally  lose  their  arsenic  on  the  simple  application  of 
heat.     This  method  may  be  especially  recommended  on 
account  of  its  simplicity,  neatness,  and  cleanness,  as  well 
as  for  the  certainty  of  its  results,  even  though  but  minute 
quantities  of  arsenic  be  present.     It  is  especially  adapted 
for  the  direct  production  of  arsenic  from  sulphuret  of  arse- 
nic, and  is,  in  this  respect,  superior  to  all  other  methods 
suggested.      The   most    exact    results    are    obtained    by 
placing  the   sulphuret  of   arsenic,  rubbed   together  with 
twelve  times  its  amount  of  a  mixture  consisting  of  three 
parts  of  dry  carbonate  of  potash,   and  one  part   of  cya- 
nide of  potassium,  into  a  glass  tube,  open  at  its  anterior 
extremity. 


The  mixture  is  best  introduced  into  the  tube  by  means  of 
a  slip  of  paper,  folded  into  the  shape  of  a  gutter.  This 
paper  containing  the  mixture  is  inserted  into  the  tube,  and 
the  latter  then  being  turned  half  way  round  its  axis,  the 
powder  falls  into  it  (at  the  spot  a  c)  without  soiling  any 
other  part.  The  tube  is  then  gently  heated  in  its  entire 
length,  transmitting  at  the  same  time  a  very  slow  stream 
of  dry  carbonic  acid  gas  (dried  by  means  of  sulphuric  acid) 
through  it,  till  all  water  is  expelled.  The  spot  b  is  then 
heated  to  a  feeble  degree  of  redness,  when,  as  this  point  is 


ARSENFOUS    ACID.  133 

attained,  the  mixture  is  heated  from  a  towards  c,  by  means 
of  a  second  lamp.  The  arsenic  condenses  at  d,  forming 
a  crust  of  admirable  purity.  In  this  manner  the  most 
distinct  metallic  mirrors  may  be  obtained,  from  one  260th 
part  of  a  grain  of  sulphuret  of  arsenic,  and  even  less. 
Fresenius  and  Babo. 

10.  If  to  arsenious  acid  (either  in  solid  form  or  in  solu- 
tion) some  acetic  acid,  and  then  some  potash  in  excess, 
be  added,  the  mixture  evaporated  to  dryness,  and  the  resi- 
due heated  to  redness  in  a  tube,  alcarsin  (Oxide  of  cacodyl. 
C4  H6  As  +  O)   will  be   formed,    which   is   immediately 
detected  by    its  characteristic  and   insupportable   odour. 
This  odour  immediately  changes  into  that  not  less  charac- 
teristic of  chloride  of  cacodyl,  when  the   contents  of  the 
tube  are  again  exposed  to  heat,  with  the  addition  of  a  few 
drops  of  protochloride  of  tin.     This  property  affords  us 
also  a  means  of  further  testing  the  metallic  crusts  obtained 
by  Marsh's  apparatus.     They  are  for  this  purpose  boiled 
with    water    containing  atmospheric  air,   till  completely 
dissolved;  acetic   acid,  and  potash    in   excess,  are   then 
addexl  to  the  solution,  which  is  evaporated  to  dryness,  the 
residue  heated  to  redness  in  a  small  tube,  and  the  further 
operation   conducted    as  just  now   stated.     BUNSEN  has 
recently  suggested  this  method  of  testing  crusts  of  arse- 
nic ;  these  are,   however,  but  slowly  dissolved  in  boiling 
water  containing  air. 

11.  If  arsenious  acid  or  an  arsenite  be  exposed  on  a 
charcoal  support  to  the  reducing  flame  of  a  blow-pipe^  a 
highly  characteristic  odour  of  garlic  will  be   perceived, 
especially  if  some  carbonate  of  soda  be  added  to  the  test 
specimen.     This  odour  is  owing  to  the  reduction  and  reox- 
idation  of  the  arsenic,  and  enables  us  to  detect  even  minute 
quantities  of  this  substance.     This  test,  however,  cannot 
be  implicitly  relied  upon.     The  garlic  odour  belongs  nei- 
ther to  the  vapour  of  arsenious  acid,  nor  to  those  of  arsenic, 
but  probably  to  a  lower  degree  of  oxidation  of  the  latter 
substance.     It  is  always  perceived  on  exposing  arsenic  to 
heat,  with  the  free  access  of  air, 

6 


134  ARSEJSIC  ACID, 


€.    ARSENIC  ACID.       (As  05J 

1.  Arsenic  acid  and  the  arseniates  are  volatile  only  at  a 
very  high  degree  of  heat.     Nearly  all  the  arseniates  are 
colourless,  and  insoluble  in  water,  with  the  exception  of  the 
alkaline  arseniates. 

2.  Sulphuretted  hydrogen  does  not  precipitate  alkaline 
and  neutral  solutions  ;  in  acid  solutions  it  produces  a  yel- 
low precipitate  of  SULPHARSENIC  ACID,  (As  Ss.)    In  dilute 
solutions  this  precipitate  is  often  formed  after  the  lapse  of 
a  considerable  time  (twenty -four  hours.)     Heat  promotes 
its  separation.     The  sulpharsenic  acid  shows  the  same 
relations  as  the  sulpharsenious  acid  to  these  solvents  and 
means  of  decomposition  which  we  have  mentioned  when 
treating  of  the  latter  substance.     If  to  a  solution  of  free 
arsenic  acid  or  of  an  arseniate,   sulphurous  acid  is  added, 
this  latter  substance  decomposes  with  the  arsenic  acid, 
giving  rise  to  the  formation  of  arsenious  acid  and  sulphuric 
acid.     If  sulphuretted  hydrogen,  and  if  needed,  an  acid  be 
then  added,  all  the  arsenic  will  immediately  precipitate  as 
sulpharsenious  acid. 

3.  Hydrosulphuret  of  ammonia  in  neutral  and  alkaline 
solutions,    converts  arsenic   acid  into    sulpharsenic  acid, 
which  remains  in  solution,  as  sulpharsenico-sulphuret  of 
ammonium.  This  compound  is  decomposed  on  the  addition 
of  an  acid,  and  sulpharsenic  acid  precipitates.     This  pre- 
cipitation is   more  rapid   than    that  from    acid   solutions 
by  means  of  sulphuretted  hydrogen.     It  is  promoted  by 
heat. 

4.  Nitrate  of  silver  produces  in  neutral  solutions  of  the 
arseniates  highly  characteristic  reddish-brown  precipitates 
of  ARSENIATE  OF  SILVER,  (3  Ag  O,  As  O5)  which  is  solu- 
ble both  in  dilute  nitric  acid  and  in  ammonia.     Ammonio- 
nitrate  of  silver  yields  the  same  precipitate  with  solutions 
of  arsenic  acid  or  arseniates. 

5.  Ammonia-sulphate  of  copper  produces  under  the  same 
circumstances  as  the  salts  of  silver,  greenish  blue   pre- 
cipitates   Of  ARSENIATE    OF    COPPER.      (2    Cu    O,    As  O  5.) 

6.  The  arseniates  present  the   same   relations  as  ihe 
arsenites  to   hydrogen,  to  carbonate  of  sodat  and   char- 
coal, to  cyanide  of  potassium  and  before  the  blow-pipe. 


ARSENIC  ACID.  135 

Recapitulation  and  remarks. — The  separation  and  safe 
detection  of  the  oxides  belonging  to  the  second  section  of 
the  sixth  group,  and  especially  of  oxide  of  tin,  presents 
difficulties  under  certain  circumstances.  The  protoxide 
of  tin  may  be  easily  and  safely  detected  by  its  reaction 
with  perchloride  of  gold,  even  in  the  presence  of  other 
oxides.  The  separation  of  peroxide  of  tin  from  oxide  of 
antimony  succeeds  pretty  well  in  the  humid  way  by  means 
of  a  hot  solution  of  bitartrate  of  potash,  or  of  a  solution  of 
free  tartaric  acid  ;  but  it  succeeds  only  when  the  peroxide 
of  tin  is  present  in  the  form  of  the  modification  obtained  by 
the  action  of  nitric  acid  on  metallic  tin.  To  obtain  this 
modification,  it  is  necessary  to  reduce  the  substance  under 
examination  by  means  of  zinc,  if  this  substance  is  not  an 
alloy  ;  in  this  reduction  the  presence  of  nitric  acid  must  be 
carefully  avoided.  The  method  of  separating  the  sulphu- 
rets  by  means  of  ammonia  gives  rise  to  errors,  as  the  higher 
degrees  of  sulphuration  of  the  antimony  are  soluble  in 
ammonia  ;  and  even  the  simple  sulphuret  of  antimony  is  not 
absolutely  insoluble  in  it,  when  mixed  with  a  trace  of  free 
sulphur,  which  cannot  easily  be  avoided.  The  presence 
of  peroxide  of  tin  is  certain  only  when  a  ductile  metallic 
grain  of  tin  is  obtained  in  the  reducing  flame ;  its  ductility 
in  this  case  enables  us  to  distinguish  it  from  antimony.  This 
reduction  is  very  easily  effected  before  the  blow-pipe  by 
means  of  a  mixture  of  equal  parts  of  cyanide  of  potassium 
and  carbonate  of  soda  ;  but  care  should  be  taken  that  the 
peroxide  of  tin  be  not  mixed  with  nitre,  which  causes  it  to 
deflagrate,  &c.  Peroxide  of  tin  and  oxide  of  antimony 
may  be  detected  before  the  blow-pipe,  even  if  combined, 
the  antimony  being  distinguished  by  its  characteristic  oxi- 
dation crust,  and  the  tin  by  its  ductility  after  the  volatili- 
zation of  the  antimony*  Inexperienced  students,  however, 
generally  fail  in  this  method.  Antimony  may,  moreover, be 
detected  by  the  decomposition  of  chloride  of  antimony  by 
means  of  water,  and  by  the  colour  of  its  sulphuret.  If  the 
sulphuret  of  antimony  is  mixed  with  a  large  proportion  of 
any  of  the  sulphur-compounds  of  arsenic,  this  latter  mark 
of  "detection  is  unsafe.  In  this  case  the  mixed  sulphurets 
may  be  heated  to  redness,  which  causes  the  sulphuret  of 
arsenic  to  volatilize  ;  and  the  residue  may  be  dissolved  in 


136  ARSENIC   ACID. 

hydrochloric  acid,  and  this  solution  again  tested  by  means 
of  sulphuretted  hydrogen. 

The  detection  of  arsenic  upon  the  whole  can  by  no 
means  be  said  to  be  difficult ;  but,  nevertheless,  frequent 
errors  take  place,  especially  if  we  content  ourselves  with 
drawing  definite  conclusions  from  individual  reactions, 
such  as  the  characteristic  odour  when  heated  on  charcoal. 
We  must,  therefore,  lay  it  down  as  a  rule  that  the  presence 
of  arsenic  can  only  be  proved  by  a  concurrence  of  the 
various  reactions,  and  especially  by  the  formation  of  me- 
tallic arsenic.  It  may  be  pretty  completely  separated  from 
tin  by  deflagrating  the  sulphurets  with  carbonate  of  soda 
and  nitre.  The  presence  of  tin  does  not,  however,  prevent 
the  detection  of  arsenic.  But  the  case  is  different  with 
antimony,  especially  in  testing  by  Marsh's  method,  which 
is  now  so  generally  followed.  A  metallic  mirror  obtained 
by  Marsh's  apparatus  ought,  therefore,  never  to  be  consi- 
dered as  a  proof  of  the  presence  of  arsenic,  if  further  tests 
do  not  give  the  most  certain  conviction  that  the  metallic 
crust  is  indeed  produced  by  arsenic.  And  this  conviction 
is  sometimes  very  difficult  to  be  obtained,  when  we  operate 
upon  very  minute  quantities,  so  that  the  formerly  used 
methods  of  reduction  are  by  far  superior  to  Marsh's  me- 
thod, as  far  as  certainty  is  concerned,  although  it  cannot 
be  denied  that  they  do  not  equal  it  in  delicacy,  nor  in 
rapidity  and  convenience.  The  complete  separation  of 
arsenic  from  antimony  may  be  effected  by  means  of  bicar- 
bonate of  ammonia,  the  simple  sulphuret  of  antimony  being 
insoluble  in  this  substance,  whilst  sulphuret  of  arsenic 
readily  dissolves  in  it.  But  this  method  of  distinction 
yields  a  positive  and  certain  result  only  in  a  few  cases, 
viz.  in  those  where  we  are  quite  sure  that  the  simple  sul- 
phuret of  antimony  cannot  be  mixed  with  a  higher  sul- 
phuret of  antimony,  nor  with  free  sulphur,  whilst  in  all 
other  cases  it  easily  gives  rise  to  mistakes.  It  is,  there- 
fore, exceedingly  well  adapted  for  the  testing  of  the 
products  of  combustion  obtained  by  means  of  Marsh's 
apparatus,  (vide  §  94,  d  7,  &,)  but  it  cannot  be  used  for  the 
separation  of  the  sulphurets  obtained  in  the  usual  way. 
And  even  less  complete  are  those  separations  of  antimony 
from  arsenic  which  are  founded  on  the  relations  of  their 


RELATIONS  OF  THE  ACIDS  TO  REAGENTS.     137 

sulphurets  to  concentrated  hydrochloric  acid  or  to  caustic 
ammonia.  The  separation  of  both  metals  from  each  other 
does  not  succeed  even  by  dissolving  the  sulphuret  in 
potash,  and  boiling  the  solution  with  oxide  of  copper.  A 
far  more  certain  result  may  be  obtained  by  deflagrating 
the  sulphurets  with  carbonate  of  soda  and  nitre,  treating 
the  mass  obtained  with  water,  filtering,  and  decomposing 
with  nitric  acid  the  basic  alkaline  antimoniates,  which  the 
filtrate  contains  in  solution  to  a  small  extent.  By  means 
of  this  process  almost  all  the  antimony  is  obtained  as  an 
insoluble,  and  all  the  arsenic  as  a  soluble  compound. 

The  presence  of  antimony  cannot  easily  give  rise  to  any 
errors  in  the  reduction  of  arsenites  or  arseniates,  by  means 
of  carbonate  of  soda  and  charcoal,  or  cyanide  of  potassium 
and  carbonate  of  soda.  The  reduction  of  sulphuret  of 
arsenic  by  means  of  cyanide  of  potassium  and  carbonate 
of  soda,  in  a  stream  of  carbonic  acid  gas,  does  not  admit 
even  of  the  possibility  of  confounding  arsenic  with  anti- 
mony, and  is  of  all  methods  best  adapted  to  yield  a  most 
conclusive  proof  of  the  presence  of  arsenic.  Nitrate  of 
silver  is  the  safest  test  for  distinguishing  arsenious  acid 
from  arsenic  acid,  in  their  aqueous  solutions.  If  extra- 
neous substances  be  contained  in  the  solution,  they  prevent 
its  being  directly  tested  for  arsenious  or  arsenic  acid ;  in 
that  case  the  solution  must  be  completely  precipitated  by 
means  of  sulphuretted  hydrogen,  and  the  sulphurets 
obtained  dissolved  in  liquor  of  potash ;  this  solution  must 
then  be  boiled  with  pure  oxide  of  bismuth,  or  with  the 
carbonate  or  basic  nitrate  of  bismuth ;  the  liquid  is  then 
filtered  off  from  the  sulphuret  of  bismuth  formed  ;  one 
part  of  the  filtered  liquid  is  tested  for  arsenious  acid  by 
means  of  sulphate  of  copper,  according  to  the  method 
described  §  94,  d  6,  and  the  other  part  for  arsenic  acid,  by 
means  of  nitrate  of  silver,  after  neutralization  with  nitric 
acid. 

B.  RELATIONS  OF  THE  ACIDS  TO  REAGENTS. 

§  95. 

We  divide  the  reagents  which  serve  for  the  determina- 
tion of  acids,  in  like  manner  as  those  used  for  the  deter- 


138  INORGANIC    ACIDS. 

mination  of  the  bases  into  GENERAL  REAGENTS,  i.  e.  such 
as  indicate  the  GROUP  to  which  the  acid  under  examina- 
tion belongs  ;  and  SPECIAL  REAGENTS,  i.  e.  such  as  en- 
able us  to  detect  the  INDIVIDUAL  ACIDS.  The  determina- 
tion and  limitation  of  the  groups  can  hardly  be  made  with 
the  same  degree  of  exactness  with  the  acids  as  with  the 
bases. 

The  two  principal  groups  into  which  acids  are  divided 
are  that  of  INORGANIC  and  that  of  ORGANIC  ACIDS.  No 
characteristic  distinction  can,  however,  be  selected  which 
is  applicable  through  the  entire  series  ;  for  we  can  neither 
select  the  ternary  composition  as  a  distinguishing  mark  of 
organic  acids,  nor  can  we  define  organic  acids  to  be  such 
as  require  for  their  formation  the  co-operation  of  the  vital 
power,  for  this  definition  not  only  leaves  us  in  doubt  as  to 
a  great  many  acids,  for  instance,  formic  acid,  uric  acid, 
&c.,  but  it  is  in  itself  altogether  unscientific,  since  all  the 
vital  processes  in  the  animal  and  vegetable  body  are,  in 
fact,  merely  modified  chemical  processes.  We  shall, 
therefore,  select,  as  the  characteristic  mark  by  which  we 
divide  organic  from  inorganic  acids,  the  properties  they 
exhibit  at  a  high  temperature,  calling  those  organic  acids, 
the  salts  of  which — (especially  those  with  alkaline  bases 
or  bases  of  the  alkaline  earths)— are  decomposed  at  a  red 
heat,  with  separation  of  carbon.  This  mark  of  distinction 
has  the  advantage  of  being  easily  perceived,  and  of  en- 
abling us  by  a  very  simple  preliminary  experiment  imme- 
diately to  decide  upon  the  principal  group  to  which  an 
acid  belongs. 

1.  INORGANIC  ACIDS. 
First  Group. 

ACIDS    WHICH    ARE    PRECIPITATED     FROM    THEIR    NEUTRAL 
SOLUTIONS     BY    CHLORIDE    OF     BARIUM  '.     ArSCUlC     Add, 

Arsenious  Acid,  Chromic  Acid,  Sulphuric  Acid,  Phos- 
phoric Acid,  Boracic  Acid,  Oxalic  Acid,  Hydrofluoric 
Acid,  Carbonic  Acid,  Silicic  Acid. 

We  subdivide  this  group  into  four  classes,  as  follow  : 
1.  Acids  which  are  decomposed,  in  their  acid  solutions, 
by  sulphuretted  hydrogen,  and  which  we  have,  there- 


CHROMIC  ACID,  139 

fore,  already  remarked  upon,  when  treating  of  the 
bases,  viz.  ARSENIOUS  ACID,  ARSENIC  ACID,  and  CHRO- 
MIC ACLD. 

S.  Acids  which  are  not  decomposed,  in  their  acid  solu- 
tions, by  sulphuretted  hydrogen,  and  the  barytes  com- 
pounds of  which  are  insoluble  in  hydrochloric  acid. 
SULPHURIC  ACID  alone  belongs  to  this  class. 

3.  Acids  which  are  not  decomposed,  in  their  acid  solu- 

tions, by  sulphuretted  hydrogen,  and  the  barytes  com- 
pounds of  which  are  dissolved  by  hydrochloric  acid, 
WITHOUT  DECOMPOSITION:  these  are  PHOSPHORIC 

ACID,  BGRACIC  ACID,  OXALIC  ACID,  and  HYDROFLUORIC. 

(Although  we  intend  to  treat  of  oxalic  acid  also  in  the 
organic  group,  yet  we  must  consider  this  acid,  in  the 
inorganic  group  too,  since  its  salts  have  the  property 
of  being  decomposed  at  a  red  heat,  without  real  car- 
bonization, and  it  might,  therefore,  easily  foe  over- 
looked as  an  organic  acid.) 

4.  Acids  which  are  not  decomposed,  in   their  acid  solu- 

tions, by  sulphuretted  hydrogen,  and  the  barytes  salts 
of  which  are  soluble  in  hydrochloric  acid,  WITH  DE- 
COMPOSITION: CARBONIC  ACID,  SILICIC  ACID. 

First    Section   of  the  First    Group    ef  the    Inorganic 

Acids. 

•§  96. 

a.  The  ARSENIOUS  ACID  and  ARSENIC  ACID,  are,  as  we 
have  stated,  decomposed  by  sulphuretted  hydrogen,  so  as 
to  separate  their  corresponding  sulphurets.  On  account 
of  this  property,  we  have  considered  them  together 
with  the  bases,  as  it  leads  to  confounding  them  with  the 
metallic  oxides  rather  than  with  other  acids*  (Vide  §  93.) 

6.  CHROMIC  ACID.  (Cr  O3.) 

1.  The  chromates  are  all  red  or  yellow  ;  most  of  them 
are  insoluble  in  water.  Some  of  them  are  decomposed  at 
a  red  heat ;  those  with  an  alkaline  base  are  fixed,  and  solu- 
ble in  water ;  the  solutions  of  the  neutral  chromates  are 
yellow,  those  of  the  acid  chromates  are  red.  These  tints 


140  CHROMIC    ACID. 

are  still  visible  in  highly  dilute  solutions.  The  yellow 
colour  of  a  neutral  solution  changes  into  red  on  the  addi- 
tion of  a  mineral  acid,  owing  to  the  formation  of  an  acid 
salt. 

2.  Sulphuretted  hydrogen  reduces  the  chromic  acid,  as 
Well  when  free  as  combined  in  solution,  so  as  to  give  rise 
to  the  formation  of  oxide  of  chromium,  water,  and  sulphuric 
acid,  with  precipitation  of  sulphur.     Heat  promotes  this 
decomposition.     If  no  free  acid  is  present,  only  a  portion 
of  the  oxide  of  chromium  formed  is  kept  in  solution  by  the 
sulphuric  acid    formed  at  the   same  time,  and  a  greenish- 
gray  precipitate   is   obtained,  consisting  of  a  mixture  of 
hydrated  oxide    of  chromium  and  sulphur.     But  if  free 
acid  is  present,  a  far  less  considerable  precipitate  of  pure 
sulphur  is  obtained.     The  salt  of  oxide  of  chromium  formed 
imparts  a  green  tint  to  the  fluid,  in  either  case. 

3.  Chromic  acid  may  be  reduced  to  chromic  oxide  by 
means  of  many  other  substances,  especially  by  sulphurous 
acid,  or  by  being  heated  with  hydrochloric  acid,  particu- 
larly on  the  addition  of  alcohol,  (whereupon  hydrochloric 
ether  and  aldehyde  escape,)  or  by  metallic  zinc,  or  by 
heating  with  tartaric  acid,  oxalic  acid,  &c.     All  these  re- 
actions are  clearly  characterized  by  the  red  or  yellow  colour 
of  the  solution  changing  into  the  green  tint  of  the   salt  of 
oxide  of  chromium. 

4.  Chloride    of  barium   produces   a  yellowish  white 
precipitate   of   CHROMATE    OF  BARYTES   (Ba   0,   Cr  03) 
which  is  soluble  in  hydrochloric  and  in  nitric  acid. 

5.  Nitrate  of  silver  produces  a  dark  purple  precipitate 
of  CHROMATE  OF  SILVER  (Ag  O,  Cr  O8.)  which  is  soluble 
in  nitric  acid  and  in  ammonia. 

6.  Acetate  of  lead  produces  a  yellow  precipitate    of 
CHROMATE  OF  LEAD  (Pb  O,  Cr  O3)  which  is  soluble  in 
potash,  and  sparingly  soluble  in  dilute  nitric  acid.     The 
yellow  colour  of  this  precipitate  changes  to  red,  on  the  ad- 
dition of  ammonia. 

7.  If  insoluble  chromates  be  fused   with  carbonate  of 
soda  and  nitre,  and  the  fused  mass  dissolved  in  water,  .a 
YELLOW  coloured  fluid  will  be  obtained,  the  colour  of  which 
is  owing  to  the  dissolved  alkaline  chromate  ;  on  the  addi- 


SULPHURIC   ACID.  141 

tion  of  an  acid,  this  colour  changes  to  red.     The  oxides 
remain  either  in  their  pure  state  or  as  carbonates* 

Remarks.— When  testing  for  bases  we  always  find  the 
chromic  acid  as  chromic  oxide,  since  sulphuretted  hydrogen 
converts  the  acid  into  the  oxide.  The  colour  of  the  solution 
is  so  characteristic,  that  a  further  testing  for  it  is  almost 
unnecessary.  If  we  have  any  reason  to  suppose  that  chro- 
mic acid  is  present  in  a  substance  under  examination,  and 
if  metallic  oxides  are  at  the  same  time  in  the  solution,  we 
prefer  reducing  the  chromic  acid  by  means  of  hydrochloric 
acid  and  alcohol,  to  effecting  this  reduction  by  sulphuretted 
hydrogen.  The  reactions  with  salts  of  silver  and  of  lead 
afford  a  safe  test  in  aqueous  solutions. 

Second  Section  of  the  First  Group  of  the  Inorganic  Acids. 

§  97. 

SULPHURIC    ACID.       (S    O3.) 

1.  The    sulphates  are,   for  the  most  part,    soluble   in 
water  ;  the  insoluble  sulphates  are  generally  white,  the 
soluble  sulphates  are  for  the  most  part  colourless  in  their 
crystalline  state.     The  sulphates  of  alkalies  and  of  alka- 
line earths  are  not  decomposed  by  a  red  heat. 

2.  Chloride   of  barium  produces  in   solutions  of  sul- 
phuric acid  and  sulphates,  even  when  extremely  dilute,  a 
heavy  white  precipitate  of  SULPHATE  OF  BARYTES  (Ba  O, 
SOa)  in  the  form  of  a  fine  powder  ;  this  precipitate  is  inso- 
luble in  hydrochloric  acid  and  in  nitric  acid. 

3.  Acetate  of  lead  produces  a  heavy,  white  precipitate 
of  SULPHATE  OF  LEAD  (Pb  O,   SO  a)  which   is  sparingly 
soluble  in  dilute  nitric  acid,  but  completely  so  in  hot  and 
concentrated  hydrochloric  acid. 

4.  Those  sulphates  which  are  insoluble  in  water  and 
acids,  are  converted  into  CARBONATES  on  being  fused  with 
alkaline  carbonates,  giving  at  the  same  time  rise  to  the 
formation  of  an  alkaline  sulphate. 

5.  The  sulphates  of  alkalies   and  alkaline  earths,  may 
be  reduced  to  sulphurets  by  being  exposed  on  charcoal  to 
the  reducing  flame  of  the  blow-pipe  either  by  themselves 

6* 


142  PHOSPHORIC    ACID. 

or  (and  with  greater  facility)  mixed  with  carbonate  of 
soda  and  charcoal.  These  sulphurets  may  be  detected  by 
the  odour  of  sulphuretted  hydrogen  which  they  emit  upon 
being  moistened  with  a  few  drops  of  an  acid.  If  this  is 
done  on  a  paper  which  has  been  previously  dipped  into  a 
solution  of  lead,  or  on  a  clean  silver  plate,  (such  as  a  po- 
lished coin,)  a  black  stain  of  sulphuret  of  lead  or  sulphuret 
of  silver  is  immediately  formed. 

Remarks. — Of  all  acids,  sulphuric  acid  is  almost  the 
easiest  to  be  detected,  by  its  characteristic  and  excessively 
sensible  reaction  with  salts  of  barytes.  It  is  only  neces- 
sary to  take  care  not  to  mistake  for  sulphate  of  barytes, 
precipitates  of  chloride  of  barium,  and  especially  of  nitrate 
of  barytes,  which  are  formed  when  aqueous  solutions  of 
these  salts  are  mixed  with  fluids  containing  a  large  pro- 
portion of  free  hydrochloric  acid  or  free  nitric  acid.  It  is 
very  easy  to  distinguish  these  precipitates  from  sulphate 
of  barytes,  as  they  immediately  disappear  again,  on  the  acid 
fluid  being  diluted  with  water.  It  is,  however,  possible 
to  be  misled  by  this  relation  to  barytes,  so  as  to  confound 
sulphuric  acid  with  hydrofluosilicic  acid.  Although  we 
have  not  treated  of  this  acid,  yet  we  may  here  as  well 
point  out,  that  should  any  doubt  exist  as  to  the  nature  of  a 
precipitate  of  barytes,  this  may  be  easily  set  at  rest  by 
treating  the  precipitate  before  the  blow-pipe,  with  carbo- 
nate of  soda  and  charcoal.  (Compare  §  97,  5.) 

Third  Section  of  the  First  Group  of  the  Inorganic  Acids . 

§  98. 

a.   PHOSPHORIC    ACID.       (PO5.) 

We  consider  here  only  the  tribasic  phosphoric  acid, 
since  this  and  its  salts  alone  are  most  frequently  employed 
in  pharmacy,  &c. ;  we  disregard  altogether  the  mono- 
basic and  bibasic  phosphoric  acid. 

1.  The  phosphates  with  a  fixed  base  are  not  completely 
decomposed  by  heat,  but  they  may  thereby  be  converted, 
according  to  the  higher  or  lower  degree  applied,  into  pyro- 
phosphates  or  metaphosphates.  Of  the  phosphates,  only 


PHOSPHORIC    ACID,  143 

those  with  an  alkaline  base  are  soluble  in  water,  in  their 
neutral  state.    The  solutions  have  an  alkaline  reaction. 

2.  Chloride  of  barium  produces  in  aqueous  solutions  of 
neutral  or  basic  phosphates,  a  white  precipitate  of  PHOS- 
PHATE OF  BARYTES  (2  Ba  O,   PO5)  which  is   soluble  in 
hydrochloric  acid  and  in  nitric  acid,  and  sparingly  solu- 
ble in  muriate  of  ammonia. 

3.  Solution  of  gypsum  produces  in  neutral  or  alkaline 
solutions,   a    white    precipitate    of   PHOSPHATE  OP  LIME 
(2  Ca  O,  PO6 )  which  is  easily  soluble  in  acids,  even  in 
acetic  acid. 

4.  Chloride  of   magnesium  or  sulphate  of  magnesia 
produce  in  neutral  or  alkaline  solutions  white  precipitates 
of  PHOSPHATE  OF  MAGNESIA  (2  Mg  O,  POs)  which  are, 
however,  perceptible  only  in  rather  concentrated  solutions, 
especially  on   the  application   of  heat.     But  if  free  am- 
monia or  carbonate   of  ammonia   be    added   to  a    even 
highly  dilute  solution,  a  white  crystalline  and  quickly  sub- 
siding precipitate  of  BASIC   PHOSPHATE   OF   MAGNESIA  AND 
AMMONIA  (2  Mg  0,  NH4  O)    (PO5+2  HO+10  aq.)  is 
formed,  which  is  insoluble  both  in  ammonia  and  in  mu- 
riate of  ammonia,  but  is  of  easy  solution  in  acids,  even  in 
acetic  acid.     This  precipitate  often  becomes  visible  only 
after  the  lapse  of  some  time  ;  agitation  promotes  its  sepa- 
ration.    (Vide  §  86,  d  5  ) 

5.  Nitrate  of  silver  throws  down  from  the  solution  of 
the  neutral  and  basic  alkaline  phosphates,  a  bright  yellow 
precipitate  of  PHOSPHATE  OF  SILVER.     (3  Ag  O  P,  O5.)    If 
the  solution  contained  a  basic  phosphate,  the  fluid  in  which 
the  precipitate  is  suspended,  manifest  a  neutral  reaction, 
whilst  it  has  an  acid  reaction  if  the  solution  contained  a 
neutral  phosphate.     This  is  owing  to  the  nitric  acid  re-  » 
ceiving  for  3  eq.  of  oxide  of  silver  which  it  yields  to  the 
phosphoric  acid,  only  2  eq.  of  alkali  and   1   eq.  of  water, 
(for  the  water  does  not  neutralize  the  characteristic  pro- 
perties of  the  acid.) 

6.  Acetate  of  lead  produces  in  neutral  and  alkaline  so- 
lutions a  white  precipitate  of  PHOSPHATE  OF  LEAD,  (2  Pb 
O,  P  O5J)   which  is  easily  soluble  in  nitric  acid,  and  al- 
most insoluble  in  acetic  acid.     By  its  behaviour  before  the 
blow-pipe  this  precipitate  affords  us  an  excellent  means  of 


J44  BORACIC   ACID. 

detecting  the  presence  of  phosphoric  acid.  For,  in  the 
first  place,  it  is  not  reduced,  or  at  least,  only  with  the  great- 
est difficulty,  on  being  exposed  on  charcoal,  even  to  the 
reducing  flame  ;  and  it  is,  in  the  second  place,  distinguish- 
ed inasmuch  as  the  transparent  and  colourless  pearl  which 
it  presents  in  the  oxidizing  flame,  crystallizes  on  cooling, 
becomes  opaque,  and  generally  shows  quite  distinct  dode- 
cahedrons. 

7.  If  to  a  hydrochloric  solution  of  a  phosphated  alkaline 
earth  perchloride  of  iron  be  added  in  excess,  and  then 
ammonia  till  the  solution  manifest  an  alkaline  reaction,  a 
bulky,  more  or  less  dark,  reddish-brown  precipitate  is  ob- 
tained, consisting  of  a  mixture  of  hydrated  peroxide  of 
iron  and  BASIC  PERPHOSPHATE  OF  IRON.  Ammonia  with- 
draws from  it  but  very  little  of  its  phosphoric  acid,  whilst 
hydrosulphuret  of  ammonia  completely  decomposes  it  into 
sulphuret  of  iron  and  phosphate  of  ammonia.  If  an  in- 
sufficient quantity  of  perchloride  of  iron,  is  used,  a 
white  precipitate  of  neutral  perphosphate  of  iron  is- 
formed,  which  redissolves  on  the  addition  of  ammonia  in 
excess. 

b.  BORACIC  ACII>.     (B  O3.) 

1.  The  aqueous  solution  of  boracic  acid  reddens  litmus 
paper,  but  it  tinges  tumeric  paper  brown.   The  borates  are 
not  decomposed  by  a  red  heat  ;  only  those  with  alkaline 
bases  are  easily  soluble  in  water.     The  solutions  are  co- 
lourless, and  all  of  them,  even  those  of  the  acid  salts  mani- 
fest an  alkaline  reaction. 

2.  Chloride  of  barium  produces  in  solutions  of  borates, 
when  not  too  highly  dilute,  a  white  precipitate  of  BORATE 
OF  BARYTES,  (Ba  O.  B  O3,)  which  is  soluble  in  acids  and 
ammoniacal  salts. 

3.  Nitrate  of  silver  produces  in  rather  concentrated 
solutions  of  borates,    a  white  precipitate   of  BORATE  OF 
SILVER,  (Ag  O,  B  O3J)  which  is  soluble  in  nitric  acid  and 
in  ammonia. 

4.  If  Sulphuric  acid  or  hydrochloric  acid  be  added  to 
highly  concentrated,  hot  solutions  of  borates,  the  BORACIC 
ACID  will  separate    on   cooling,   in  the   form  of   shining 
crystalline  scales. 


OXALIC    ADID.  145 

5.  If  free  boracic  acid  or  a  borate — (in  which  latter  case 
the  boracic  acid  must  be  liberated  by  the  addition  of 
sulphuric  acid) — be  ignited  with  alcohol,  the  flame  will  ap- 
pear of  a  very  distinct  YELLOWISH-GREEN  colour,  especially 
on  stirring  the  mixture,  owing  to  the  boracic  acid  evapor- 
ating together  with  the  alcohol,  and  becoming  incandes- 
cent in  the  flame.  This  reaction  becomes  most  sensible, 
if  the  cup  containing  the  mixture  is  first  heated,  the  alco- 
hol then  ignited,  allowed  to  burn  for  a  short  time,  then  ex- 
tinguished and  rekindled.  At  the  first  flickering  of  the 
flame  its  borders  appear  green  in  that  case,  even  though 
the  quantity  of  the  boracic  acid  be  so  minute  as  to  produce 
no  perceptible  colouring  of  the  flame,^  when  treated  in  the 
usual  manner. 

c.  OXALIC  ACID.     (O  =  C2  O3.) 

1 .  All  the  oxalates  are  decomposed  at  a  red  heat,  owing 
to  the  oxalic  acid  decomposing  into  carbonic  acid  and  car- 
bonic oxide.     Those  which  have  an  alkali  or  an  alkaline 
earth  for  their  base,  are  in  this  process  converted  into  car- 
bonates (without  separation  of  carbon,  when  pure  ;)  those 
with  a  metallic  base  leave  the  metal  behind   either  in  its 
metallic  state  or  as  an  oxide,  according  to  the   degree  of 
reducibility  of  the  metallic  oxide.     The  alkaline  oxalates 
are  soluble  in  water,  and  so  are  some  oxalates  with  metal- 
lic base. 

2.  Chloride  of  barium  produces  in  the  neutral  solutions 
of  oxalates,  a  white  precipitate  of  OXALATE  OF  BARYTES, 
(Ba  O,O  +  aq.,)  which  is  soluble  in  nitric  acid  and  in  hy- 
drochloric acid,  but  is  more  sparingly  soluble  in  ammoniacal 
salts  than  bSrate  of  barytes. 

3.  Nitrate  of  silver  produces  in  neutral  solutions   of 
oxalates,  a  white  precipitate  of  OXALATE  OF  SILVER,  (Ag 
O  6,)  which  is  soluble  in  nitric  acid  and  in  ammonia. 

4.  Lime-water,  and  all  the  soluble  salts  of  lime,  and  thus 
also  solution  of  gypsum,  produce  in  even  highly  dilute 
solutions  of  free  oxalic  acid  or  of  oxalates,  precipitates  of 
OXALATE  OF  LIME,  (Ca  O,  6  +  2  aq.)  in  the  form  of  a  fine 
white  powder,  which  readily  dissolve  in  hydrochloric  acid 
and  in  nitric  acid,  but  are  almost  insoluble  in  oxalic  acid, 
and  in  acetic  acid.     The  presence  of  ammoniacal  salts  does 


146  HYDROFLUORIC    ACID. 

not  at  all  prevent  the  formation  of  these  precipitates.  The 
addition  of  ammonia  considerably  promotes  the  precipitation 
of  the  free  oxalic  acid,  by  salts  of  lime. 

5.  If  oxalic  acid  or  an  oxalate  in  a  dry  state  be  heated 
with  concentrated  sulphuric  acid  in  excess,  the  latter  with- 
draws from  the  oxalic  acid  its  necessary  constitutional 
water,  the  oxalic  acid  is  decomposed  into  CARBONIC  ACID 
and  CARBONIC  OXIDE,  and  both  these  gases  escape  with 
effervescence.  If  the  quantity  operated  upon  is  not  too 
minute,  the  escaping  carbonic  oxide  gas  may  be  kindled ; 
it  burns  with  a  blue  flame.  If  in  this  reaction  the  sulphuric 
acid  assumes  a  dark  tinge,  it  is  a  sign  that  the  oxalic  acid 
contained  an  admixture  of  some  organic  substance. 

d.      HYDROFLUORIC    ACID.       (H  Fl.) 

1 .  Hydrofluoric  acid  is  distinguished  from  all  other  acids 
by  its  property  of  dissolving  the  insoluble  modification  of 
silicic  acid,  as  well  as  the  silicates  insoluble  in  hydrochloric 
acid,  giving  rise  to  the  formation  of  fluoride  of  silicon,  and 
of  water.     The  hydrofluoric  acid  decomposes  in  the  same 
manner  with  metallic  oxides,  giving  rise  to  the  formation 
of  fluorides  and  of  water.     The  fluorides  of  the  alkaline 
metals  are  soluble  in  water ;  those  corresponding  with  the 
alkaline  earths  are  either  not  at  all  or  but  very  sparingly 
soluble  in  water;  floride  of  aluminum  is  easily  soluble. 
Most  of  the  fluorides  corresponding  with  the  oxides  of  the 
heavy  metals  are  very  sparingly  soluble  in  water,  such  as, 
for  instance,  fluoride  of  copper,  fluoride  of  lead,  fluoride  of 
zinc ;  many  other  fluorides  are  of  easy  solution  in  water,  as, 
for  instance,  perfluoride  of  iron,  fluoride  of  tin,  perfluoride 
of  mercury,  &c.     Of  those  compounds  which  are  either 
insoluble  or  but  sparingly  soluble  in  water,  many  dissolve 
in  free  hydrofluoric  acid,  whilst  others  remain  undissolved. 
Most  of  the  fluorides  do  not  undergo  decomposition,  when 
heated  to  redness  in  a  crucible. 

2.  If  to  the  aqueous  solution  of  hydrofluoric  acid  or  of  a 
fluoride,  chloride  of  calcium  be  added,  FLUORIDE  OF  CAL- 
CIUM, (Ca  Fl,)  is  obtained  in  the  form  of  a  gelatinous  pre- 
cipitate, which  is  so  transparent,  as  at  first  to  induce  the 
belief,  that  the  fluid  has  remained  clear  and  unaltered.    The 
addition  of  ammonia  promotes  the  complete  separation  of 


HYDROFLUORIC    ACID.  147 

this  precipitate,  which  is  insoluble  in  hydrochloric  acid  and 
nitric  acid,  as  well  as  in  alkaline  fluids  when  cold ;  a  minute 
quantity  is,  however,  dissolved  on  boiling  with  hydrochloric 
acid.  It  is  scarcely  more  soluble  in  free  hydrofluoric  acid 
than  in  water. 

3.  If  any  fluoride,  reduced  to  a  fine  powder,  be  mixed 
with  pounded  glass  or  sand,  and  the  mixture  be  drenched 
in  a  test  tube,  with  concentrated  sulphuric  acid  and  heat 
applied,  FLUOSILICIC  GAS  (Si  F13)  is  evolved,  giving  rise  to 
dense  white  fumes  in  the  air  when  the  latter  contains  moisture. 
If  the  gas  be  transmitted  through  water — (by  means  of  a  bent 
tube  fitted  to  the  test  tube) — silicic  acid  separates  in  a  gel- 
atinous form,  whilst  the  fluid  becomes  strongly  acid,  owing 
to  the  formation  of  hydrofluosilicic  acid.    (Compare  §  43.) 

4.  If  a  plate  of  glass  be  covered  with  bees-wax,  which 
can  readily  be  done  by  heating  it  and  allowing  the  wax  to 
spread  equally  over  the  surface,  and  lines  be  traced  on  it 
with  a  point,  (which  should  not  be  too  hard,  a  point   of 
wood  answers  best,)  and  the  plate  be  then  covered  with 
the  solution  of  a  fluoride  mixed  with  sulphuric  acid,  and 
allowed  to  dry,  the  lines  exposed  will  be  found,  on  remov- 
ing the  wax,  to  be  etched  upon  the  glass.     If  we  have 
but  very  minute  quantities  to  test,  the  acid  solution  of  a 
fluoride  mixed  with  sulphuric  acid   is,   at  a  gentle  heat, 
evaporated  to  dryness,  in  a  watch  glass  ;  after  washing  off 
the  salt  mass  remaining,  the  internal  surface  of  the  glass 
appears  dimmed. 

5.  If  a  fluoride,  reduced  to  a  fine  powder,  no  matter 
whether  soluble  or  insoluble,  is  drenched,  in  a  platinum 
crucible,  with  concentrated  sulphuric  acid»  and  the  cruci- 
ble, being  covered  with  a  glass  plate,  prepared  as  stated 
above,  is  exposed  fifteen  minutes  or  half-an-hour  to  a  gentle 
heat,  taking  always  care  not  to  melt  the  wax,  the  exposed 
lines  are  found  engraved  after  the  removal  of  the  wax.     If 
the  quantity  of  hydrofluoric  acid  evolved  by  means  of  the 
sulphuric  acid  was  very  minute,  the  etching  frequently  is 
not  perceived,  after  the  removal  of  the  wax ;  but  if  the 
glass  be  breathed  upon,  the  exposed  lines  become  visible 
again,  owing  to  the  unequal  capacity  of  condensing  water, 
which  the   etched    and  untouched    parts    of   the    plate 
possess. 


148  HYDROFLUORIC    ACID. 

Remarks.  —  The   third   section   contains,    as  we   have 
stated,  phosphoric  acid,  boracic  acid,  oxalic  acid  and  hydro- 
fluoric acid.     The  barytes  compounds  of  these  acids,  as  we 
have  seen,  are  dissolved  by  hydrochloric  acid,  without  de- 
composition ;  alkalies,  therefore,  precipitate  them  unaltered, 
by  neutralizing  the  hydrochloric  acid.     The  barytes  com- 
pounds of  arsenious  acid,  arsenic  acid,  and  chromic  acid, 
present  the  same  property,  and  must,  therefore,  if  present,  be 
removed  before  any  conclusion,  as  to  the  presence  of  phos- 
phoric acid,  boracic  acid,  oxalic  acid,  or  hydrofluoric  acid, 
can  be  drawn  from  this  precipitation  of  a  salt  of  barytes. 
But  even  without  regard  to  this  point,  no  great  value  can  be 
placed  on  their  reaction,  not  even  for  the  detection  of  these 
acids,  and  far  less  for  their  separation  from  other  acids, 
since  the  salts  of  barytes  in  question,  and  especially  the 
borate  of  barytes,  are  not  precipitated  from  their  hydro- 
chloric solutions,  by  ammonia,  if  the  quantity  of  free  acids 
present  is  to  any  extent,  or  if  any  ammoniacal  salt  in  a  cer- 
tain quantity   is  present.     Boracic   acid  may  always  be 
delected  by  the  tint  which  it  communicates  to  the  flame  of 
alcohol,  if  care  is  taken  that  the  solution  be  sufficiently  con- 
centrated before  the  addition  of  the  alcohol,  and  when  the 
substance  under  examination  is  a  borate,  that  it  be  mixed 
with  a  sufficient  quantity  of  sulphuric  acid  (best  concen- 
trated).    If  the  boracic   acid  is  free,   it  should  first   be 
combined  with  an  alkali  when  evaporating  its  solution, 
or  else  a  large  portion  of  it  will  volatilize  with  the  vapours 
of  the  water.     The  phosphoric  acid  is  sufficiently  charac- 
terized by  the  yellow  silver  precipitate,  by  the  character- 
istic properties  of  the  basic  phosphate  of  magnesia  and 
ammonia,  (especially  the  insolubility  of  this  compound  in 
sal  ammoniac,)  and  finally,  by  the  behaviour  of  phosphate 
of  lead  before  the  blow-pipe.     Perchloride  of  iron  is  un- 
doubtedly the  best  means  of  decomposing  those  phosphates 
which  have  an  alkaline  earth  for  their  base,  after  they  have 
been   dissolved  in  hydrochloric  acid.     Oxalic  acid  may 
always  easily  be  detected  by  solution  of  gypsum,  if  we 
only  keep  in  view,  that  the  precipitate  thereby  formed 
must  not  disappear  on  the  addition  of  acetic  acid,  (herein 
it  is  distinguished  from  phosphoric  acid,)  and  must  readily 
dissolve  in  dilute  hydrochloric  acid,  and.be  converted  into 


CARBONIC    ACID.  149 

carbonate  of  lime  on  the  application  of  a  red  heat,  (herein 
it  differs  from  hydrochloric  acid).  The  oxalates  of  the 
alkaline  earths  are  completely  decomposed  by  boiling 
with  carbonate  of  soda.  Lastly,  the  hydrofluoric  acid 
cannot  easily  be  confounded  with  other  acids ;  since, 
under  all  circumstances,  it  is  certainly  detected  by  its 
property  of  etching  glass.  The  most  sensitive  results  are 
always  obtained  by  treating  solid  fluorides  with  sulphuric 
acid. 

Fourth  Section  of  the  First  Group  of  Inorganic  Acids. 

§99. 

6%    CARBONIC    ACID.       (CO2.) 

1.  The  carbonates  lose  a  part  of  their  carbonic  acid,  at  a 
red    heat.     All   carbonates    or   colourless   oxides  appear 
white  or  colourless.     Only  those  with  an  alkaline  base 
are  soluble   in  water,  in  their  neutral  stale.     Their  solu- 
tions have  a  very  strong  alkaline  reaction.     Further,  the 
bi-carbonates  with  alkaline  bases,  those  also  which  have 
an  alkaline  earth  for  their  base,  and  some  with  metallic 
bases,  are  soluble  in  water. 

2.  The  carbonates  are  decomposed  by  all  free  acids  so- 
luble in  water,  with  the  exception  of  hydrocyanic  acid  and 
hydrosulphuric  acid.     In  this  process,   the  carbonic  acid 
escapes  with  effervescence,  as  a  colourless  and  almost  in- 
odorous gas,  which  imparts  a   transient    reddish   tint   to 
litmus  paper.     It  is  necessary  to  use  the  decomposing  acid 
in  excess,  especially  when  operating  upon  a  salt  with  an 
alkaline  base,    since    frequently   no   effervescence   takes 
place,  when  adding  the  acid  in  too  small  a  quantity,  owing 
to  the  formation  of  acid  carbonates. 

3.  Lime-water    and    water  of  barytes  produce,  when 
brought  into  contact  with  carbonic  acid   or   soluble   car- 
bonates, white    precipitates   of  NEUTRAL  CARBONATE  OP 
LIME  or  BARYTES.     When  testing  for  free  carbonic  acid, 
the  reagent  ought  always  to  be  employed  in  excess,  as  the 
acid  carbonates  of  the  alkaline  earths  are  soluble  in  water. 
The  precipitates  formed  dissolve  in  acids,  with  efferves- 


150  SILICIC    ACID. 

cencej  and  are  not  precipitated  again  by  ammonia,  after 
the  complete  expulsion  of  the  carbonic  acid,  by  boiling. 

4.  Chloride  of  calcium  and  chloride  of  barium  yield 
with  neutral  alkaline  carbonates  immediately,  and  with  bi- 
carbonates  only  on  boiling,  precipitates  of  CARBONATE  OF 
LIME  or  of  BARYTES.  These  reagents  yield  no  precipi- 
tate with  free  carbonic  acid. 

b.  SILICIC  ACID.     (Si  03.) 

1.  Silicic  acid  occurs  in  two  modifications,   the  one  is 
soluble  in  acids  and  water,  the  other  is  affected  only  by 
hydrofluoric  acid.     The  soluble  modification  is  converted 
by  heat  into  the  insoluble.     If  the  insoluble  modification  is 
fused  with  pure  alkalies  or  alkaline   carbonates,  a   basic 
alkaline  silicate  is  produced,  which  is  soluble  in  water  and 
from  which  acids  separate   the  silicic   acid  in   its  soluble 
modification.     The  soluble  modification  readily  dissolves 
when  boiled  with  solution  of  potash,  the  insoluble  modi- 
fication dissolves  only  very  slowly  in  the  same  menstruum. 
The  silicates  of  the  alkalies  alone  are  soluble  in  water. 

2.  The  solutions  of  the  alkaline  silicates  are  decomposed 
by  all  acids  ;  when  the  solutions  are  highly  concentrated 
the  SILICIC  ACID  precipitates  in  the   form  of  gelatinous 
flakes,  whilst  it  remains  dissolved  in  more  dilute  solutions. 
If  a  solution  of  this  kind,  mixed  with  an  acid,  (hydrochloric 
acid  or  nitric  acid,)  is  evaporated  to  dryness,  the  silicic 
acid  is  converted  from  its  soluble  into  its  insoluble  modi- 
fication, and  remains,  therefore,  as  a  white  gritty  powder, 
on  the  residue  being  treated  with  water. 

3.  In  the  silicates  which  have  an  earth  or  a  metal  for 
their  base,  the  silicic  acid  is  also  present  either  in  its  solu- 
ble or   in   its   insoluble  modification.     The  silicates  with 
the  soluble  modification  are  decomposed  by  boiling  hydro- 
chloric or  nitric  acid,  the  silicic  acid  separating  as  a  gela- 
tinous hydrate,  and  the  decomposing  acid  combining  with 
the  base.     But  on  silicates  with  the  insoluble  modification, 
these  acids  have  no  action ;  in  order  to  separate  the  silicic 
acid  from  its  base,  such  silicates  must  be  either  treated  in 
the  humid  way,  with  hydrofluoric  acid,  or  fused  with  al- 
kaline carbonates. 


INORGANIC  ACIDS.  151 

4.  Carbonate   of  soda  dissolves  a  large  proportion  of 
silicic  acid  in  the  flame  of  the  blow-pipe,  forming  SILICATE 
OF  SODA  as  a  colourless  glass,  which  remains  transparent 
on  cooling;  the  carbonic  acid  escapes  with  effervescence. 
Inexperienced  students  often  fail  in  obtaining  a  clear  glass, 
because  they  use  too  much  carbonate  of  soda  in  propor- 
tion to  the  quantity  of  the  test  specimen. 

5.  Phosphate  of  soda  and  ammonia  leave  silicic  acid 
almost  entirely  undissolved.    The  silicic  acid  floats  about 
as  an  opaque  mass  in  the  transparent  glass,  and  may,  there- 
fore, be  perceived  with  greater  facility  in  the  glass  when 
red  hot  than  after  cooling.     The  silicates  present  the  same 
property  ;  the  phosphate  of  soda  and  ammonia  withdraws 
their  base  from  them,  and  separate  silicic  acid.  The  bases 
are  dissolved,  whilst  the  silicic  acid  remains  undissolved. 

Recapitulation  and  Remarks. — Carbonic  acid  is  generally 
very  easily  detected  by  its  salts  evolving  an  almost  inodorous 
gas  when  treated  with  acids.  We  transmit  the  gas  through 
lime-water  or  water  of  barytes,  when  operating  upon  com- 
pounds which  evolve  other  gases  at  the  same  time.  Silicic 
acid  in  its  soluble  modification,  (into  which  it  must  always 
be  converted  first,)  is  detected,  under  all  circumstances,  by 
supersaturating  its  compounds  with  hydrochloric  acid, 
evaporating  to  dryness.  treating  the  residue  with  water,  and 
testing  the  undissolved  part  before  the  blow-pipe. 

Second  Group  of  Inorganic  Acids. 

ACIDS   WHICH    ARE    PRECIPITATED    BY  NITRATE  OF    SILVER, 

BUT  NOT  BY  CHLORIDE  OF  BARIUM  i  Hydrochloric  Acid, 
Hydrobromic  Acid,  Hydriodic  Acid,  Hydrocyanic  Acidt 
Hydrosulphuric  Acid. 

§  100. 

All  the  silver  compounds  of  the  oxides  belonging  to 
this  gronp  are  insoluble  in  dilute  nitric  acid.  The  acids  of 
this  group  decompose  with  metallic  oxides,  so  as  to  give 
rise  to  the  combination  of  the  metals  with  the  metalloids, 
whilst  the  oxygen  of  the  oxide  at  the  same  time  combines 
with  the  hydrogen  of  the  acid  forming  water. 


152  HYDROBROMIC   ACID. 


a.    HYDROCHLORIC    ACID.       (Cl  H.) 

1.  The  chlorides  are  easily  soluble  in  water,  with  the 
exception  of  chloride  of  lead,  chloride  of  silver,  and  pro- 
tochloride  of  mercury  ;  most  of  the  chlorides  are  white  or 
colourless.  Many  of  them  volatilize  at  a  high  temperature, 
without  decomposition  ;  many  chlorides  are   decomposed 
at  a  red  heat,  and  but  few  of  them  are  fixed. 

2.  Hydrochloric  acid,  and  solutions  of  chlorides,  yield 
with  nitrate  of  silver,  even  when  highly  dilute,  white  pre- 
cipitates of  CHLORIDE  OF  SILVER,  (Ag   Cl,)  which,  when 
exposed  to  light,  change  first  into  a  violet  colour  and  then 
into  a  black  ;  these  are  readily  soluble  in  ammonia,  insolu- 
ble in  nitric  acid,  and   fuse  without  decomposition  when 
heated.  (Vide  §  90,  a  4.) 

3.  Protonitrate  of  mercury  and  acetate  of  lead  pro- 
duce  in   solution,    containing  free  hydrochloric    acid   or 
chloride,   precipitates   of  CHLORURET   OF  MERCURY  (Hg2 
Cl)  and  CHLORIDE  OF  LEAD  (Pb  Cl.)     For  the  properties 
of  these  precipitates,  vide  §  90,  b  4,  and  §  90,  c  4. 

4.  When  chlorides  are  heated  with  manganese  and  sul- 
phuric acid,  chlorine  is  evolved,  which  is   easily  detected 
by  its  YELLOWISH-GREEN  colour,  and  its  odour. 

5.  If  a   chloride  be  rubbed    together  with  chromate  of 
potash,  and  the  mixture  be   drenched  with  concentrated 
sulphuric  acid,  in  a  tubular  retort,  and  gentle  heat  applied, 
a  deep  brownish-red  gas  will  be  copiously  evolved  ;  (CHRO- 
MATE    OF    PERCHLORIDE    OF    CHROMIUM,    Cr     Cl    +   2    Cr 

O3  ;)  this  gas  condenses  into  a  fluid  of  the  same  colour, 
and  passes  over  into  the  receiver.  If  this  chromate  of 
perchloride  of  chromium  is  mixed  with  ammonia  in  excess, 
a  yellow -coloured  liquid  is  obtained,  owing  to  the  forma- 
tion of  chromate  of  ammonia ;  this  yellow  colour  changes 
into  a  reddish  yellow,  on  the  addition  of  an  acid,  owing 
to  the  formation  of  acid  chromate  of  ammonia. 

6.    HYDROBROMIC    ACID.    (Br  H.) 

1.  The  bromides  have,  in  general,  a  great  analogy  with 
the  chlorides,  in  insolubility  and  in  their  relations  when 
exposed  to  heat. 


HYDROBROMIC    ACID.  153 

2.  Nitrate  of  silver  produces  in  aqueous  solution  of 
hydrobromic  acid  and  bromides  a  yellowish-white  precipi- 
tate of  BROMIDE  OF  SILVER,  (Ag  Br,)  which  is  insoluble 
in  dilute  nitric  acid,  and  somewhat  sparingly  soluble  in 
ammonia. 

3.  Nitric  acid  decomposes  hydrobromic  acid  and  the 
bromides,  with  the  application  of  heat,  liberating  bromine, 
by  oxidizing  the  hydrogen  or  the  metal.     The  liberated 
bromine   colours   the  solution  yellowish-red  ;  but  if  we 
operate  upon  a  bromide  in  a  solid  form,  yellowish  red 
vapours  of  bromine  gas  escape,  with  the  odour  of  chlo- 
rine ;  these  vapours,  when  present  in  sufficient  quantity, 
condense  in  the  cold  part  of  the  test-tube  into  small  drops. 

4.  Chlorine,  or  solution  of  chlorine,  also  liberates  bro- 
mine in  solutions  of  its  compounds ;  the  fluid  assuming  a 
yellowish-red  tint,  if  the  quantity  of  the  bromine  present 
is  not  too  minute.     If  a  yellow-coloured   solution  of  this 
kind  be  agitated  with  ether,  it  becomes  colourless  ;  all  the 
bromine  dissolves  in  the  ether,  which  appears  distinctly 
yellow,  even  though  but  a  very  minute  quantity  of  bromine 
be  present.     If  the  etherial  solution  of  bromine  be  agitated 
with  some  solution  of  potash,  the  yellow  tint  vanishes,  and 
we  have  bromide  of  potassium  and  bromate  of  potash  in 
solution.     If  the  solution  be  then  evaporated,  and  the  resi- 
due heated  to  redness,  the  bromate  of  potash  is  converted 
into  bromide  of  potassium.     This  substance  may  be  fur- 
ther tested  as  follows  : 

5.  If  bromides  are  heated  with  manganese  and  sulphuric 
acid,  YELLOWISH-RED  VAPOURS   OF  BROMINE  are  evolved, 
If  the  bromine  is  present  only  in  very  minute  quantity,  the 
colour  of  their  vapours  may  not  be  visible.     The  experi- 
ment, in  that  case,  must  be  conducted  in  a  small  retort, 
and  the  vapours  passing  over  transmitted  through  a  long 
condensing   glass   tube   into  small   test-tubes,   containing 
some  starch,  for  if 

6.  Moist  starch  is  brought  into  contact  with  free  bro- 
mine, no  matter  whether  in  solution  or  in  gaseous  form, 
YELLOW  BROMIDE  OF  STARCH  is  formed.     The  colouring 
does  not  always  take  place  immediately.     The  reaction  is 
rendered  most  delicate  by  closing  the  test-tube  which  con- 
tains the  starch  drenched  with  the  fluid  under  examina- 
tion, before  a  spirit-lamp,  and  then  inverting  it,  so  that 


154  HYDRIODIC    ACID. 

the  moist  starch  becomes  placed  above  the  liquid.  The 
slightest  trace  of  bromine  will  then,  after  twelve  to  twenty- 
four  hours,  impart  a  yellow  tinge  to  the  starch.  This 
colour  vanishes  again  on  the  tube  being  allowed  to  stand 
for  a  longer  time. 

7.  If  a  mixture  of  a  bromide  and  of  chromate  of  potash 
be  drenched  with  sulphuric  acid,  and  heat  applied,  a 
brownish-red  gas  is  evolved,  just  as  is  the  case  with  the 
chlorides.  But  this  gas  consists  of  pure  BROMINE,  and  the 
fluid  passing  on,  therefore,  becomes  not  yellow,  but  colour- 
less, when  supersaturated  with  ammonia. 

C.    HYDRIODIC    ACID.    (I  H.) 

1.  The  iodides  also  correspond,  in  many  respects,  with 
the  chlorides..     Of  those,  however,  which  contain  heavy 
metals,  by  far  more  are  insoluble  in  water  than  is  the  case 
with  the  chlorides.     Many  iodides  present  characteristic 
tints. 

2.  Nitrate  of  silver  produces  in  aqueous  solutions  of 
hydriodic  acid  and  of  iodides,  yellowish  white  precipitates 
of  IODIDE  OF  SILVER,  (Ag  I,)  which  blacken  when  exposed 
to  light,  are  insoluble  in  dilute  nitric  acid,  and  very  spar- 
ingly soluble  in  ammonia. 

3.  A  solution   of  one  part  of  sulphate  of  copper,  and 
two  and  a  quarter  parts  of  sulphate  of  iron,  precipitates 
from  aqueous  neutral  solutions  of  the  iodides,  PROTIODIDE 
OF  COPPER,  (Cu?  I,)  in  the  form  of  a  dirty-white  precipi- 
tate.    The  addition  of  some  ammonia  promotes  the  com- 
plete precipitation  of  the  iodine.     Chlorides  and  bromides 
are  not  precipitated  by  this  reagent. 

4.  Nitric  acid  decomposes  the  hydriodic  acid  and  the 
iodides  in  the  same  manner  as  the  bromides.     Colourless 
solutions  of  hydriodic  acid  or  of  the  iodides  are,  therefore, 
immediately  coloured  BROWNISH-YELLOW  by  nitric   acid, 
even  at  a  low  temperature ;    and  from  concentrated  solu- 
tions the  IODINE  separates  as  a  BLACK  PRECIPITATE,  whilst 
nitric  oxide  gas  escapes  with  effervescence.    Solid  iodides, 
when  heated  with  nitric  acid,  evolve,  besides  the  nitric  acid 
gas  VIOLET  vapours  of  iodine,  which  condense  on  the  colder 
parts  of  the  vessel  into  a  blackish  sublimate. 

5.  Chlorine  and  solution  of  chlorine,  liberate  iodine  from 


HYDROCYANIC    ACID.  155 

its  combinations,  but  the  liberated  iodine  combines  with 
these  reagents  when  they  are  added  in  excess,  forming  a 
colourless  CHLORIDE  OF  IODINE. 

6.  If  iodides  are   heated  with  concentrated  sulphuric 
acid,  or  with  sulphuric  acid  and  manganese,  IODINE  be- 
comes liberated,  and  may  be  easily  detected  by  the  violet 
colour  of  its  gas.     If  concentrated  sulphuric  acid  alone  has 
been  used,  sulphurous  acid  is  evolved  at  the  same  time.    If 
the  quantity  of  the  iodine  present  is  very  minute,  it  can  no 
longer  be  detected  by  the  colour  of  its  gas,  and  we  have 
recourse  to  the  test  with  starch,  as  follows : 

7.  If  to  a  solution  of  iodine  or  of  hydriodic  acid,  or  of  an 
iodide,  (the  iodine  in  the  latter  must  first  be  liberated  by 
means  of  nitric  acid,)  thin  starch  paste  be  added,  a  more  or 
less  blackish-blue  tint  or  precipitate  of  IODIDE  OF  STARCH 
is  formed,  even  though  but  the  most  minute  traces  of  iodine 
be  present.     When  solution  of  chlorine  is  employed  for 
the  liberation  of  the  iodine,  it  ought  to  be  added  very  cau- 
tiously, as,  owing  to  the  formation  of  chloride  of  iodine,  the 
blue  tint  does  not  appear,  or  at  least  manifests  itself  only 
after  the  addition  of  sulphuretted  hydrogen,  protochloride  of 
tin,   or  some  other  means  of  reduction.     Even  the  most 
minute  traces  of  iodine  in  dry  compounds  of  any  description, 
may  be  detected  most  safely  by  means  of  starch,  in  the 
following  manner.     The  substance  under  examination  is 
drenched  in  a  retort,  with  concentrated  nitric  acid,  and  the 
retort  loosely  closed  with  a  stopper,  to  which  a  moistened 
slip  of  paper,  or,  better  still,  a  moistened  strip  of  white  cot- 
ton cloth,  imbued  with  starch,  is  attached ;  after  a  few  hours 
this  will  appear  blue,  even  though  but  the  most  minute 
trace  of  iodine  be  present. 

8.  The  iodides  present  the  same  relation  to  chromate  of 
potash  and  sulphuric  acid  combined,  as  to  sulphuric  acid 
alone.     (Compare  §  100,  a  5.) 

d-       HYDROCYANIC    ACID.       (Cy  H.) 

1 .  Those  cyanides  which  have  an  alkali  or  alkaline  earth 
for  their  base,  are  soluble  in  water,  as  hydrocyanates.  They 
are  easily  decomposed  by  acids,  even  by  carbonic  acid,  but 
are  not  decomposed  by  heat  when  the  access  of  air  is  pre- 
vented. When  fused  with  the  oxide  of  lead,  of  copper,  of 


156  HYDROCYANIC   ACID. 

antimony,  of  tin,  and  many  other  oxides,  they  reduce  these 
oxides,  and  are  converted  into  cyanates.  Only  a  few  of 
those  cyanides  which  contain  heavy  metals  are  soluble  in 
water ;  all  of  them  are  decomposed  at  a  red  heat,  giving 
rise  either  to  the  formation  of  cyanogen  and  metals,  as  the 
cyanides  of  the  noble  metals,  or  of  nitrogen  gas  and  carbo- 
nates, as  the  cyanides  of  the  other  heavy  metals.  Many 
combinations  of  cyanogen  with  heavy  metals  are  not  de- 
composed by  dilute  oxygen  acids,  and  with  difficulty  by 
concentrated  nitric  acid.  Hydrochloric  acid  and  sulphur- 
etted hydiogen  decompose  most  of  them  easily  and  com- 
pletely. Cyanogen  combines  with  several  metals,  (iron, 
manganese,  cobalt,  chromium,)  forming  compound  radicals, 
in  which  these  metals  cannot  be  detected  by  many  of  the 
usual  methods. 

2.  Nitrate  of  silver  produces,  in  solutions  of  free  hydro- 
cyanic acid  and  of  alkaline  hydrocyanates,  white  precipitates 
of  CYANIDE  OF  SILVER,  (Ag  Cy,)  which  are  easily  soluble 
in  cyanide  of  potassium,  somewhat  difficult  of  solution  in 
ammonia,  and  insoluble  in  dilute  nitric  acid  ;  these  precipi- 
tates  are  decomposed  at  a  red  heat,   leaving   the  pure 
metallic  silver  behind; 

3.  If  to  the  solution  of  an  alkaline  hydrocyanate,  solution 
of  sulphate  of  iron,  which  has  been  for  some  time  in  contact 
with  the  air,  (magnetic  oxide  of  iron ,)  is  added,  a  precipi- 
tate or  tint  of  PRUSSIAN  BLUE  is  formed.     (Compare  §  88, 
f  5.)     Free  hydrocyanic  acid,  to  be  detected  in  this  manner, 
must,  therefore,  first  be  combined  with  an  alkali.     If  the 
alkali  is  present  in  excess,  hydrated  magnetic  oxide  of  iron 
is  precipitated  beside  the  Prussian  blue ;  in  that  case  this 
latter  precipitate  must  first  be  redissolved  by  hydrochloric 
acid,  before  the  blue  colour  of  the  precipitate  can  appear 
clearly  and  distinctly. 

3.  If  to  a  solution  of  hydrocyanic  acid,  potash  be  added 
in  excess,  and  then  finely  pounded  peroxide  of  mercury  ^ 
the  latter  substance  readily  dissolves  just  as  well  as  in  free 
hydrocyanic  acid.     As  peroxide  of  mercury  is  soluble  in 
an  alkaline  fluid  only  in  presence  of  hydrocyanic  acid,  it 
follows  that  by  means  of  this  reaction  we  can  safely  detect 
the  presence  of  hydrocyanic  acid. 

4.  The  cyanogen  cannot  be  detected  in  cyanide  of  mer^ 


HYDROSULPHURIC    ACID.  157 

cury  by  any  of  these  methods.  To  detect  it  in  this  combi- 
nation, we  add  hydrochloric  acid  and  metallic  iron  to  a 
solution  of  cyanide  of  mercury.  Metallic  mercury  is  sepa- 
rated in  this  process,  and  hydrocyanic  acid  and  protochloride 
of  iron  formed,  (which  latter  substance  is  partly  converted 
into  perchloride  of  iron,  on  exposure  to  the  air,)  If  an 
alkali  is  then  added  to  the  fluid,  Prussian  blue  is  formed, 
the  colour  of  which,  however,  becomes  distinct  only  after 
having  removed,  by  the  addition  of  hydrochloric  acid,  the 
excess  of  the  hydrated  magnetic  oxide  of  iron  present 
Cyanide  of  mercury  may  also  be  easily  decomposed  by 
sulphuretted  hydrogen,  giving  rise  to  the  formation  of 
sulphuret  of  mercury  and  hydrocyanic  acid.  When  heated, 
the  cyanide  of  mercury  decomposes,  as  we  have  already 
stated,  (I,)  into  metallic  mercury  and  cyanogen,  which 
latter  substance  may  be  detected  by  its  characteristic  effect 
on  the  olfactory  organs. 

5.  In  the  ferrocyanides  and  ferricyanides  with  alkaline 
bases,  the  presence  of  these  compound  radicals  may  be 
easily  detected,  in  the  former  by  solutions  of  protoxide  of 
iron,  or  solution  of  copper,  and  in  the  latter  by  solution  of 
peroxide  of  iron.  Free  hydrocyanic  acid  may  be  obtained 
from  these  cyanides  by  distilling  them  with  sulphuric  acid. 
The  insoluble  ferrocyanides  and  ferricyanides  are  decom- 
posed by  being  heated  with  caustic  potash  or  carbonate  of 
potash,  giving  rise  to  the  formation  of  ferrocyanide  of 
potassium,  and  the  separation  of  the  metals  either  as  car- 
bonates or  as  pure  oxides. 

6.    HYDROSULPHURIC    ACID.       (H  S.) 

Sulphuretted  Hydrogen  Gas. 

1 .  Only  those  sulphurets  are  soluble  in  water  which  have 
an  alkali  or  an  alkaline  earth  for  their  base.  These  as  well 
as  those  which  contain  metals  of  the  fourth  group,  (such 
as  iron,  manganese,  &c.,)  are  decomposed  by  dilute  min- 
eral acids,  with  evolution  of  sulphuretted  hydrogen  gas, 
which  may  easily  be  detected  by  its  odour,  and  by  its 
action  on  solution  of  lead.  (Vide  infra  2.)  If  the  sulphu- 
ret is  of  a  higher  degree  of  sulphuration,  a  white  precipi- 
tate of  minutely  divided  sulphur  is  formed  at  the  same 
time,  which  can  easily  be  distinguished  from  similar  pre* 


15&  HYDROSULPHURIC  ACIF. 

cipitates  by  its  inflammability*  Part  of  the  sulphurets  of 
the  fifth  and  sixth  group  are  decomposed  by  concentrated 
and  boiling  hydrochloric  acid,  with  evolution  of  sulphuret- 
ted hydrogen  gas,  whilst  others  are  not  dissolved  by  hy- 
drochloric acid,  but  by  concentrated  and  boiling  nitric  acid- 
The  combinations  of  sulphur  with  mercury  resist  both 
these  acids,  but  dissolve  readily  in  aqua  regia.  On  the  so- 
lution of  sulphurets  in  nitric  acid,  and  in  aqua  regia,-  sul- 
phuric acid  is  formed  ;  amj  in  most  cases,  moreover,  sul- 
phur separates,  which  is  easily  detected  by  its  colour  and 
behaviour  when  heated. 

2.  If  sulphuretted  hydrogen  in  solution,  or  in  a  gaseous 
form,  is  brought  into  contact  with  nitrate  of  silver  or  ace- 
tate of  lead,  black  precipitates  of  SULPHURET  OF  SILVER 
and  SULPHURET  OF  LEAD  are  formed.    (Vide  supra,  §  89,  a, 
and  §  89  c.)     If  the  odour  of  sulphuretted  hydrogen  isr 
therefore,  not  sufficient  for  its    detection,   these  reagents 
•will  afford  the   surest  proof  of  its  presence.     When  the 
sulphuretted  hydrogen  is  in  a  gaseous  form,  a  small  slip  of 
paper,  moistened  with  solution  of  lead,  is  placed  in  the  air 
to  be  tested  ;    if  sulphuretted   hydrogen  is  present,    this 
paper  will  become  covered  with  a  thin,  brownish-black  and 
lustrous  film  of  sulphuret  of  lead. 

3.  If  sulphurets  are  exposed  to  the  oxidizing  flame  of 
the  blow-pipe,  their  sulphur  burns  with  a  blue  flame,  emitting 
at  the  same  time  the  well-known  odour  of  sulphurous  acid.. 

Recapitulation  and  remarks. —  Most  of  the  acids  of  the 
first  group  are  precipitated  by  nitrate  of  silver  ;  but  these 
precipitates  will  not  be  confounded  with  the  silver  com- 
pounds of  the  acids  of  the  second  group,  as  the  former  are 
soluble  in  dilute  nitric  acid,  whilst  the  latter  are  insoluble 
in  that  fluid.  The  presence  of  hydrosulphuric  acid  pre- 
vents us  more  or  less  from  testing  for  the  other  acids  of  the 
second  group  ;  this  acid  must,  therefore,  if  present,  first  be 
removed  previous  to  testing  for  the  other  acids.  This  re- 
moval may  be  effected  by  mere  boiling,  if  the  hydrosul- 
phuric acid  is  free,  but,  if  combined  with  an  alkali,  by  the 
addition  of  a  metallic  salt,  which  does  not  precipitate  the 
other  acids,  or  at  least  not  from  acid  solutions.  Hydriodic 
and  hydrocyanic  acid  may  be  detected  even  in  the  presence 


NITRIC    ACID.  159 

of  hydrochloric  or  hydrobromic  acid,  by  the  reactions  with 
starch  and  magnetic  oxide  of  iron,  which  are  as  charac- 
teristic as  they  are  delicate.  But  the  detection  of  chlorine 
and  bromine  is  more  or  less  difficult  in  presence  of  iodine 
and  cyanogen.  These  latter  substances,  if  present,  must, 
therefore,  be  removed  first,  before  we  can  test  for  chlorine 
and  bromine.  The  separation  of  cyanogen  is  easily  effected 
by  heating  to  redness  the  silver  compounds  of  the  group. 
Cyanide  of  silver  decomposes  at  a  red  heat,  whilst  chloride, 
bromide,  and  iodide  of  silver  undergo  no  decomposition. 
Iodine  may'  be  separated  from  bromine  and  chlorine,  by 
treating  the  silver  compounds  with  ammonia,  as  the  iodide 
of  silver  is  almost  insoluble  in  this  substance.  But  the 
separation  is  more  perfect  by  precipitating  the  iodine  as 
protiodide  of  copper,  whilst  chlorine  and  bromine  remain 
in  solution.  Bromine  may  be  detected  and  distinguished 
from  chlorine,  by  mixing  the  compound  containing  both 
substances  with  hydrochloric  acid  and  chloride  of  lime,  or 
with  solution  of  chlorine,  and  absorbing  the  liberated 
bromine  by  ether.  Chlorine  may  be  detected  when  pre- 
sent with  bromine,  by  the  reaction  with  carbonate  of 
potash  and  sulphuric  acid. 

Third  Group  of  the  inorganic  Acids. 

ACIDS    WHICH    ARE    PRECIPITATED    NEITHER    BY    SALTS    OP 
BARYTES   NOR    SALTS    OF    SILVER  '.    Nitric   Add,   CkloriC 

Acid. 

§  101. 

a.  NITRIC  ACID.     (N05.) 

1.  All  the  neutral  salts   of  nitric  acid  are  soluble  in 
water  ;  only  a  few  basic  nitrates  are  insoluble  in  water. 
All  nitrates  are  decomposed  at  a  strong  red  heat.     Those 
with  alkaline  bases  yield  oxygen  and  nitrogen :  the  other 
salts,  oxygen  and  nitrous  acid. 

2.  If  a  nitrate  is  thrown  upon  red-hot  charcoal,  or  if 
charcoal  or  some  organic  substance,  paper,  for  instance,  is 
brought  into  contract  with  a  nitrate  in  fusion,  DEFLAGRA- 
TION takes  place,  i.  e.  the  charcoal  burns  at  the  expense  of 
the  oxygen  of  the  nitric  acid,  with  vivid  scintillations, 


160  CHLORIC    ACID. 

3.  If  a  nitrate  is  mixed  with  cyanide  of  potassium  in 
powder   and  the  mixture  heated  on  a  platinum  plate,  a 
vivid  DEFLAGRATION  takes  place  combined  with  distinct 
ignition  and  feeble  detonation.     Even  very  minute  quan- 
tities of  nitrates  may  be  detected  by  this  reaction. 

4.  If  the  solution  of  a  nitrate  be  mixed  with  one-fourth 
part  of  its  quantity  of  concentrated  sulphuric  acid,  and  a 
chrystal  of  protosulphate  of  iron  be  thrown  into  the  mix- 
ture, the  fluid  immediately  surrounding  this  crystal  will 
assume  a  DEEP  BROWN  TINT.    This  tint  generally  vanishes 
by  merely  agitating  the  fluid,  and  always  after  the  applica- 
tion of  heat  for  some  time.    In  this  process,  the  nitric  acid 
is  decomposed  by  the  protoxide  of  iron,  three-fifths  of  its 
oxygen  combine  with  the  protoxide,  and  convert  a  portion 
of  it  into  peroxide,  and  the  remaining  nitric  oxide  combines 
with  the  remaining  protoxide   of  iron,  forming  a  charac- 
teristic compound,  which  dissolves  in  water  producing  a 
brownish-black  colour. 

5.  If  to  the  solution  of  a  nitrate  some  sulphuric  acid  be 
added,  and  as  much  solution  of  sulphate  of  indigo  as  to 
make  the  fluid  appear  of  a  feeble  light-blue  colour,  and  the 
mixture  be  then  heated  to  boiling,  this  blue  tint  will  disap- 
pear, owing  to  the  indigo  becoming  oxidized  at  the  expense 
of  the  oxygen  of  the  nitric  acid  liberated  by  the  sulphuric 
acid ;  the  fluid  becomes  colourless,  or  assumes  a  feeble 
yellowish  tint.     Several  other  substances,  especially  free 
chlorine,  cause  the  same  discoloration,  which  ought  to  be 
especially  borne  in  mind. 

6.  If  a  nitrate  is  mixed  with  copper  filings,  and  the 
mixture  drenched  with  concentrated  sulphuric  acid,  in  a 
text  tube,  the  air  in  the  tube  assumes  a  yellowish  red  tint, 
owing  to  the  nitric  oxide  gas  which  becomes  free  on  the 
oxidation  of  the  copper  by  the  nitric  acid,  combining  with" 
the  oxygen  of  the  air,  and  forming  nitrous  acid. 

b.  CHLORIC  ACID.       (Cl  Os.) 

1.  All  chlorates   are  soluble   in  water.     When  heated 
to  redness,  their  oxygen  escapes  completely,  leaving   chlo- 
rides behind, 

2.  When  heated  with  charcoal  or   some  organic  sub- 


CHLORIC   ACID.  161 

stance)  the  chlorates  DEFLAGRATE,  and  this  with  by  far 
greater  violence  than  the  nitrates. 

3.  If  the  chlorate  is  mixed  with  CYANIDE  OF  POTASSIUM, 
and  the  mixture  heated  on  a  platinum  plate,  DEFLAGRATION 
takes  place,  with  strong  detonation  and  the  appearance  of 
flame,  even  though  the  chlorate  be  present  only  in  a  very 
minute  quantity. 

4.  Free  chloric  acid  oxidizes  and  discolours  indigo  in 
the  same  manner  as  nitric  acid  ;  if.  therefore,  the  solution 
of  a  chlorate  is  mixeckwith  sulphuric  acid  and    solution 
of  indigo,  the  phenomena  manifest  themselves,  which  we 
have  described  when  treating   of  nitric   acid,   (vide  su- 
pra, a  5.) 

5.  If  chlorates  be  heated  with   hydrochloric  acid,  the 
constituents  of  both  acids  are  mutually  decomposed,  giving 
rise  to  the  formation  of  water,  chlorous  acid  and  chlorine, 
which  latter  substances  may  easily  be  detected  by  their 
odour  and  their   greenish  colour.     (Cl   H+C1  O3  =  Cl 
O4  +  C1+HO.) 

6.  If  a  chlorate  be  drenched  with  concentrated  sulphuric 
acid,  two-thirds  of  the  metallic  oxide  are  converted  into  a 
sulphate,  and  the  other  third  into  a  hyperchlorate,  whilst 
chlorous  acid  escapes,  which  is  characterized  by  its  odour 
and  greenish  colour.     [3  (KO,  Cl  O J  +2  S03  =  2  (KO, 
2  SO3)+KO,  Cl  O7  +  2  (Cl  04.)  ]'    The  application  of 
heat  must  be  avoided  in  this  experiment,  and  small  quanti- 
ties only  operated  upon,  or  else  the  decomposition  might 
take  place  with  great  violence,  so  as  to  occasion  an  ex- 
plosion. 

Recapitulation  and  remarks. — Of  the  reactions  which 
have  been  suggested  for  the  detection  of  nitric  acid,  those 
with  sulphate  of  iron  and  sulphuric  acid,  and  with  copper 
filings  and  sulphuric  acid,  give  the  safest  results,  for  de- 
flagration with  charcoal,  detonation  with  cyanide  of  potas- 
sium, and  discolouration  of  solution  of  indigo  take  place, 
as  we  have  stated  also  when  chlorates  are  present  instead 
of  nitrates.  These  latter  reactions,  therefore,  are  decisive 
only  when  no  chloric  acid  is  present.  The  best  test  to 
ascertain  whether  chloric  acid  be  present  or  not,  is  to  heat 


162  TARTARIC    ACID. 

the  test  specimen  to  redness,  dissolving  it  and  then  testing 
its  solution  with  nitrate  of  silver. 

If  a  chlorate  be  present,  it  is  converted  into  a  chloride, 
on  being  heated  to  redness,  and  a  precipitate  of  chloride  of 
silver  is  obtained,  on  testing  the  solution  with  nitrate  of 
silver.  But  this  test  is  thus  simple  only  when  no  chloride 
is  present  at  the  same  time.  But  if  the  latter  is  the  case, 
nitrate  of  silver  must  be  added  as  long  as  any  precipitate  is 
formed ;  the  supernatant  liquid  is  then  filtered  from  this 
precipitate,  evaporated  to  dryness,  and  the  residue  heated 
to  redness.  The  results  obtained  by  the  fusion  of  chlorates 
with  cyanide  of  potassium  are  less  certain.  The  violence 
and  detonation,  with  which  the  deflagration  takes  place, 
render  it,  however,  scarcely  possible  to  confound  the  chlo- 
rates with  nitrates. 

II.  ORGANIC  ACIDS. 

First  Group. 

ACIDS  WHICH  ARE  PRECIPITATED  BY  CHLORIDE  OF  CAL- 
CIUM :  Oxalic  Acid)  Tartaric  Acid,  Par  alar  tar  ic  Acid, 
Citric  Acid,  Malic  Acid. 

§  102. 
None  of  these 'acids  volatilize  without  decomposition. 

a.  OXALIC  ACID. 
.   For  the  reactions  of  oxalic  acid  we  refer  to  §  98  c. 

b.    TARTARIC    ACID.       (T  =  (C8  H4  O10.) 

1.  The  combinations  of  tartaric  acid  with  alkalies,  as 
well  as  with  those  metallic  oxides  which  are  weak  bases, 
are  soluble  in  water*     All  tartrates  insoluble  in  water  are 
dissolved  by  hydrochloric  acid. 

2.  The  tartaric  acid  and  the  tartrates  carbonise  when 
heated  to  redness,  emitting  a  perfectly  characteristic  odour. 
The  salts  which  have  an  alkali  or  alkaline  earth  for  their 
base,  are  in  this  process  converted  into  carbonates. 

3.  If  to  a  solution  of  tartaric  acid,  or  to  that  of  a  tartrate, 
solution  of  peroxide  of  iron,  protoxide  of  manganese,  or 


PARATARTARIC    ACID,  163 

and  then  ammonia  or  potash  be  added,  no  preci- 
pitation takes  place  of  peroxide  of  iron,  protoxide  of  man- 
ganese or  alumina,  since  the  new-formed  double  tartrates 
are  not  decomposed  by  alkalies.  Tartaric  acid  prevents 
also  the  precipitation  of  several  other  oxides  by  alkalies. 

4.  Free  tartaric  acid  yields,  with  a  salt  of  potash,  and 
best  with  acetate  of  potash,  a  sparingly  soluble  precipitate 
of  BITARTRATE  OF  POTASH  (KO,  HO,  t).     The  same  pre- 
cipitate is  formed,  if  acetate  of  potash  and  free  acetic  acid, 
or   bisulphate  of  potash,   be  added  to  a  neutral  tartrate. 
When  using  bisulphate  of  potash,  we  must  be  careful  not 
to  add  it  in  excess.     The  acid  tartrate  of  potash  readily 
dissolves  in  alkalies   and  mineral  acids ;  tartaric  acid  and 
^acetic  acid  do  not  increase  its  solubility  in  water.     Violent 
agitation  greatly  promotes  the  precipitation  of  tartar. 

5.  Chloride  of  calcium  throws  down  from  the  solutions 
of  neutral   tartrates,  TARTRATE  OF  LIME  as  a  white  preci- 
pitate.    The  presence  of  amrnoniacal   salts  prevents  the 
formation  of  this  precipitate  more  or  less*     The  precipi- 
tate of  tartrate  of  lime  dissolves  to  a  clear  fluid,  in  cold  and 
dilute  solution  of  caustic  potash.     If  this  solution  is  boiled, 
the  dissolved  tartrate  of  lime  separates  in  the  form  of  a 
gelatinous  precipitate.     On  cooling,  the  solution  becomes 
clear  again. 

6.  Lime-water  produces  in  solutions  of  neutral  tartrates, 
or  even  in  solutions  of  free  tartaric  acid,  when  added  till 
an  alkaline  reaction  manifests  itself,  white  precipitates  of 
TARTRATE  OF  LIME  (f ,  2  Ca  O  8  aq.)  which  readily  dis- 
solve in  tartaric  acid.     This  precipitate  of  tartrate  of  lime 
dissolves  with  the  greatest  facility  in  solution  of  sal  am- 
moniac, and  separates  from  this  solution   only  after  the 
lapse  of  several  hours,  in  the  form  of  small  crystals,  depo- 
sited on  the  sides  of  the  vessel. 

7.  Solution  of  gypsum  does  not  produce  any  precipi- 
tate in  a  solution  of  tartaric  acid,  and  causes  only  a  minute 
precipitate  after  the  lapse  of  some  time  in  the  solution  of 
a  neutral  tartrate. 

C.  PARATARTARTC  ACID.  (RACEMIC  ACID.)  R  =  (C4  H2  O5.) 

1 .  The  relations  which  paratartrates  present  to  solvents, 
and  their  behaviour  when  heated,  are  very  analogous  to 


164  CITRIC    ACID. 

those  of  the  tartrates,  prevent,  like  the  latter,  the  precipi- 
tation by  alkalies  of  protoxide  of  manganese,  peroxide  of 
iron,  alumina,  &c. 

2.  Paratartaric  acid  has  the  same  relations  to  salts  of 
potash,  as  tartaric  acid.     The  precipitate  of  acid  paratar^ 
trate  of  potash  is  as  difficult  of  solution  as  tartar. 

3.  Chloride  of  calcium  precipitates  from   the  solutions5 
of  free  as  well  as  of  combined  paratartaric  acid,  PARATAR- 
TRATE  OF  LIME,  as  a  shining  white  powder.     This  preci- 
pitate is  not  soluble  in  sal  ammoniac.     Cold  and  concen- 
trated solution    of  potash  dissolves  it  completely,   dilute 
solution  of  potash  only  partly  \  this  solution  becomes  turbid 
and  gelatinous,  on  boiling,  and  clear  again  on  cooling. 

4.  Lime-water   produces    in    the    solutions    of  neutral 
paratartrates,  instantaneously,  white  precipitates  of  PARA- 
TARTRATE  OF  LIME.     (R,  Ca  O  +  4  aq.)     It  yields  the 
same  precipitate  with  a  solution  of  paratartarie  acid,  when 
added,  till  an  alkaline  reaction  becomes  manifest.     "When 
added  in  a  smaller  proportion,  so  that  the  solution  still  re- 
mains acid,  this  precipitate  is  formed  only  after  the  lapse 
of  a  few  moments.     Paratartrate  of  lime  is  insoluble  in  pa- 
ratartaric acid  as  well  as  in  tartaric  acid ;  when  it  is  dis- 
solved in  hydrochloric  acid,  and  ammonia  added  in  excess, 
it  precipitates  again  instantaneously,  or  at  least  after  the 
lapse  of  a  few  moments. 

6.  Solution  of  gypsum  does  not  instantaneously  produce 
a  precipitate  in  a  solution  of  "paratartaric  acid  ;  after  ten  or 
fifteen  minutes,  however,  paratartrate  of  lime  precipitates  ; 
in  solutions  of  neutral  paratartrates  the  precipitation  is  in-- 
stantaneous. 

7.  If  crystallized  paratartaric  acrd,  or  a  paratartrate  is 
heated  with  concentrated  sulphuric  acid,  the  latter  assumes 
a  black  tinge,  owing  to  the  evolution  of  sulphurous  acid  and 
carbonic  oxide  gas.     Tartarie  acid  has  the  same  property. 

d.  CITRIC  ACID.     (Ci  =  (C12  H  On.) 

1.  The  citrates  with  alkaline  bases  are  ea&ly  soluble  in 
water,  as  well  in  their  neutral  as  in  their  acid  stale;  the 
same  is  the  case  writh  the  combinations  of  citric  acid  with 
such  of  the  metallic  oxides  as  are  weak  bases.  Citric  acid 
prevents  the  precipitation  of  peroxide  of  iron,  protoxide  of 


CITRIC    ACID.  165 

manganese,  alumina,  &c.,  in  the  same  manner  as  tartaric 
acid. 

2.  Citric  acid  and  the  citrates  carbonize  when  heated  to 
redness,  emitting  pungent  acid  vapour,  which  maybe  easily 
distinguished  by  their  odour  from  those  caused  by  the  com- 
bustion of  tartaric  acid. 

3.  Chloride  of  calcium  produces  no  precipitate  in  a  solu- 
tion of  citric  acid,  not  even  on  boiling.     But  if  the  free  acid 
be  saturated  with  potash  or  soda,  a  precipitate  of  NEUTRAL 
CITRATE  OF  LIME  (ci,  3  Ca  O,  4  aq,)  is  formed  instanta- 
neously.   This  precipitate  is  insoluble  in  potash,  but  readily 
dissolves  in  solution  of  sal  ammoniac.     If  this  solution  in 
sal  ammoniac  is  boiled,  a  white  and  heavy  precipitate  of 
BASIC  CITRATE  OF  LIME  (ci,  3  Ca  O  +  Ca  O  +  aq.)  separates 
immediately.     If  a  solution  of  citric  acid,  mixed  with  chlor- 
ide of  calcium,  be  saturated  with  ammonia,  no  precipitate 
will  be  formed  at  a  low  temperature,  (if  the  solution  was 
not  highly  concentrated.)     But  if  the  clear  fluid  be  then 
boiled,  a  white,  heavy  precipitate  of  basic,  citrate  of  lime 
separates  suddenly. 

4.  Lime-water  produces  no  precipitate  in  a  cold  solution 
of  citric  acid  or  of  a  citrate.     But  on  heating  the  solution 
to  boiling  with  excess  of  lime-water,  a  white  precipitate  of 
BASIC  CITRATE  OF  LIME  is  formed,  which  disappears  again 
on  cooling. 

5.  If  to  a  solution  of  citric  acid,  acetate  of  lead  be  added 
in  excess,  a  white  precipitate  of  CITRATE  OF  LEAD  (ci,  3 
Pb  O,  aq.)  is  formed,  which  is  very  sparingly  soluble  in 
ammonia,  but  easy  of  solution  in  citrate  of  ammonia.     A 
precipitate  of  citrate  of  lead  is  equally  formed,  on  adding 
citric  acid  in  excess  to  a  solution  of  neutral  acetate  of  lead. 
This  precipitate  readily  redissolves  on  the  addition  of  am- 
monia.    We  have  just  now  seen  that  the  citrate  of  lead  is 
very  sparingly  soluble  in  ammonia  ;  this  solution  therefore 
is  not  caused  by  the  ammonia,  but  by  the  new  citrate  of 
ammonia. 

6.  If  citric  acid  or  a  citrate  is  heated  with  concentrated 
sulphuric  acid,  carbonic  oxide  gas  and  carbonic  acid  escape 
first,  without  simultaneous  blackening  of  the  sulphuric  acid ; 
but  after  boiling  for  some  time,  the  solution  becomes  dark 
coloured,  and  sulphurous  acid  escapes. 

7* 


166  MALIC    ACID. 

€.  MALIC  ACID.       (M    =  (C8  H4  O8.) 

1.  Malic  acid  forms  with  most  bases,  salts  soluble  in 
water.    The  acid  malate  of  potash  is  not  of  difficult  solution 
in  water.     Malic  acid  prevents  the  precipitation  of  the  pe- 
roxide of  iron,  &c.  by  alkalies,  in  the  same  manner  as  tar- 
taric  acid. 

2.  When  heated  to  200°  Reaumur,  malic  acid  is  de- 
composed into  MALEIC  ACID  and  HUMARIC    ACID.      This 
property  is   highly  characteristic.     If  the  experiment  is 
made  in  a  spoon,  pungent  acid  vapours  of  maleic  acid  are 
evolved  with   froth,   but  if  conducted  in  a  tube,    these 
vapours  condense  in  the  cold  part  of  the  tube,  forming 
crystals.     The  fumaric  acid  remains  behind. 

3.  Chloride  of  calcium  produces  no  precipitates,  neither 
in  solutions  of  free  malic  acid,  nor  in  those  of  the  malates. 
But  if  after  the  addition  uf  chloride  of  calcium,  alcohol  is 
added  to  the  solution  of  a  malate,   MALATE  OF  LIME,  (M, 
2Ca  O)  immediately  precipitates  as  a  white  powder. 

4.  Lime-water  precipitates   neither  the   free   nor  the 
combined  malic  acid. 

5.  Acetate  of  lead  throws  down  from  solutions  of  malic 
acid  and  of  malates,  a  white  precipitate  of  MALATE  OF  LEAD 
(M,  2Pb  O,  6  aq.)     This  precipitate  is  distinguished,  1st, 
by  losing  its  curdiness,  and  changing  into  concentrically- 
grouped^needles,  with  the  lustre  of  mother-o'-pearl,  when 
the  fluid  is  allowed  to  'stand  for  some  time;  and,   2d,  by 
its  meltingpoint  being  lower  than  the  boiling  point  of  water. 
On  heating,  therefore,  the  fluid  wherein  this  precipitate  is 
suspended  to  the  boiling  point,  the  precipitate  fuses  and 
resembles  resin  which  has  been  melted  under  water. 

6.  On  heating  malic  acid  with  concentrated  sulphuric 
acid,  the  latter  substances  become  black  with  evolution  of 
sulphurous  acid. 

Recapitulation  and  remarks. —  Of  the  organic  acids  of 
this  group,  the  tartaric  acid  and  paratartaric  acid  are  suffi- 
ciently characterized  by  the  sparing  solubility  of  their  acid 
salts  of  potash,  by  the  relation  of  their  lime  salts  to  solution 
of  potash,  and  by  the  characteristic  odour  which  they  emit 
during  their  combustion.  Tartaric  acid  may  be  distin- 


'    MALIC    ACID.  167 

guished  from  paratartaric  acid  best  by  means  of  its  combina- 
tion with  lime,  since  tartrate  of  lime  is  soluble  in  free  tartaric 
acid,  and  also  in  solution  of  sal  ammoniac,  and  thus  pre- 
sents two  properties,  which  are  wanting  in  paratartrate  of 
lime.  The  paratartaric  acid,  moreover,  differs  from  tar- 
taric acid  in  its  relation  to  solution  of  gypsum.  This 
relation  to  a  certain  extent  assimilates  paratartaric  acid  to 
oxalic  acid  ;  it  does  not,  however,  give  rise  to  any  mistake 
when  operating  upon  the  free  acids,  since  the  precipitate 
which  solution  of  gypsum  produces  in  solutions  of  para- 
tartaric acid,  is  never  formed  instantaneously.  The  oxa- 
lates,  moreover,  are  easily  to  be  distinguished  from  the 
paratartrates  by  the  properties  they  exhibit  when  heated 
either  by  themselves  or  with  sulphuric  acid-  Citric  acid 
is  best  detected  by  its  relations  to  lime-water,  or  to  chloride 
of  calcium  and  ammonia. 

The  sparing  solubility  of  the  washed  citrate  of  lead  in 
ammonia,  distinguishes  citric  acid  from  tartaric  and  para- 
tartaric acid.  The  other  re-agents  which  produce  preci- 
pitates or  other  alterations  in  its  solutions,  such  as  chloride 
of  gold,  and  salts  of  silver  and  mercury,  &c.,  show  the 
same  or  similar  relations  to  tartaric  and  paratartaric  acid, 
and,  therefore,  do  not  afford  us  safe  means  of  distinguishing 
citric  acid  from  the  two  latter  substances.  Malic  acid 
would  be  sufficiently  characterized  by  the  properties  which 
malate  of  lead  presents  when  heated  under  water,  if  this 
re-action  were  of  greater  sensibility,  and  if  it  were  not 
prevented  so  easily  by  the  presence  of  other  acids.  The 
precipitation  of  malate  of  lime  by  alcohol  can  only  be  of 
value  for  the  detection  of  malic  acid,  when  we  have  previ- 
ously convinced  ourselves  of  the  absence  of  all  other  acids, 
the  lime  salts  of  which  are  sparingly  soluble  in  water,  and 
quite  insoluble  in  alcohol,  such,  for  instance,  as  sulphuric 
acid  or  boracic  acid.  It  is,  however,  always  necessary 
further  to  test  the  precipitate  produced  by  alcohol.  The 
heating  of  malic  acid  in  a  glass  tube  leads  to  the  most 
certain  result ;  this  test  is,  however,  not  applicable  under 
all  circumstances. 


168  BENZOIC    ACID. 

Second  Group  of  the  Organic  Acids. 

ACIDS,  WHICH  ARE  UNDER  NO  CONDITION  WHATEVER  PRE- 
CIPITATED BY  CHLORIDE  OF  CALCIUM,  BUT  ARE  PRECI- 
PITATED FROM  THEIR  NEUTRAL  SOLUTIONS  BY  PERCHLOt- 

RIDE  OF  IRON  i  Succimc  aoid,  Benzoic  acid. 

§  103, 
a.  SUCCINJC  ACID,     s  =  (C4  H2  O3.) 

1.  Pure  succinic  acid  is  inodorous,  dissolves  readily  ire 
water,  and  volatilizes  completely  when  heated.     The  offi- 
cinal acid,  which  has  an  empyreumatic  odour,  leaves  a 
small  carbonaceous  residue.     The  succinates  are  decom- 
posed at  a  red  heat,  with  the  exception  of  succinate  of 
ammonia ;  those  which  have  an  alkali  or  alkaline  earth  for 
their  base,  are  converted  inta  carbonates  in  this  process. 
Most  of  the  succinates  are  soluble  in  water ;  succinic  acid 
enters  into  insoluble  or  sparingly  soluble  combinations  only 
with  the  metallic  oxides  which  are  weak  bases. 

2.  Perchloride  of  iron  produces,  in  a  solution  of  succinic 
acid  brownish  pale  red,  bulky  precipitate  of  PERSUCCINATE 
OF  IRON  (Fe2  O3,.  3s).    To  render  this  precipitation  com- 
plete, the  free  acid  must  first  be  neutralized  with  ammonia. 
Persuccinate  of  iron  readily   dissolves  in   acids,    and  is 
decomposed  by  ammonia;  the  hydrated  peroxide  of  iron 
separates,  in  this  process  of  decomposition,  and  succinic 
acid  dissolves  as  succinate  of  ammonia. 

3.  Acetate  of  lead  yields  with  succinic  acid  a  white  pre- 
cipitate of  SUCCINATE  OF  LEAD  (Pb  O,  s)  which  is  soluble 
in  succinic  acid  in  excess,  in  solution  of  acetate  of  lead,  and 
in  acetic  acid. 

4.  Protonitrate  of  mercury  and  nitrate  of  silver  aTso 
precipitate  the  succinates ;  these  precipitates,  however,  are 
by  no  means  characteristic. 

5.  The  alkaline  succinates  are  insoluble  in  alcohol. 

b.     BENZOIC  ACID.     (§e=Bz  O  =C14  H5  (X.) 

1 .  Pure  benzoic  acid  appears  in  the  form  of  white  scales 
or  needles,  or  merely  as  a  crystalline  powder.  It  volatili- 
zes completely  when  heated.  Its  vapours  cause  a  peculiar 


BENZOIC    ACID.  169 

irritating  sensation  in  tne  throat,  and  provoke  coughing. 
The  common  officinal  benzoic  acid  has  the  odour  of  benzoin, 
and  on  being  heated,  leaves  a  small  carbonaceous  residue. 
The  benzoates  of  the  alkalies  and  alkaline  earths,  are  con- 
verted into  carbonates  by  heat.  Benzoic  acid  is  very 
sparingly  soluble  in  cold  water,  but  of  pretty  easy  solution 
in  hot  water  and  in  alcohol.  It  forms  with  most  oxides 
salts  soluble  in  water,  and  enters  into  insoluble  or  sparingly 
soluble  combinations  only  with  those  oxides  which  are  weak 
bases. 

2.  Benzoic  acid  shows  the  same  relation  to  chloride  of 
iron  as  succinic  acid.  The  PERBENZOATE  OF  IRON,  (Fe2, 
O3,  See,)  is  however  by  far  brighter  and  more  yellow  than 
the  succinate.  Ammonia  decomposes  it  in  like  manner  as 
the  succinate.  When  treated  with  stronger  acids,  the  latter 
combine  with  the  peroxide  of  iron,  and  the  benzoic  acid,  on 
account  of  its  sparing  solubility,  separates  as  a  white 
precipitate. 

2-  If  to  the  solution  of  a  benzoate  a  strong  acid  be  added, 
the  benzoic  acid  is  expelled,  and  separates  in  the  form  of  a 
shining  white,  sparingly  soluble  powder.  The  benzoic 
acid  separates  in  the  same  manner  from  its  soluble  salts, 
as  already  stated,  2,)  if  some  stronger  acid  is  added  to  these 
salts  which  forms  soluble  salts  with  the  bases  with  which 
the  benzoic  acid  was  combined. 

Acetate  of  lead  does  not,  or  at  least  not  immediately, 
precipitate  the  free  benzoic  acid  nor  the  benzoate  of  ammo- 
nia, but  it  precipitates  benzoates  with  fixed  alkaline  bases, 
in  the  form  of  white  flakes. 

5.  The  alkaline  benzoates  are  soluble  in  alcohol. 

Recapitulation  and  R emarks.—  Succinic  and  benzoic 
acid  are  distinguished  from  all  other  acids  by  their  ready 
volatility  and  their  relation  to  perchloride  of  iron.  They 
differ  from  each  other  in  the  colour  of  their  persalts  of  iron, 
but  especially  in  their  solubility,  succinic  acid  being  readily 
soluble,  whilst  benzoic  acid  is  very  difficult  of  solution. 
Benzoic  acid  may,  moreover,  be  detected  by  its  irritating 
and  cough-provoking  vapours.  Succinic  acid  is  generally 
not  quite  pure,  and  may,  therefore,  also  be  detected  by  its 
odour  of  oil  of  amber. 


170  ACETIC   ACID. 

A  separation  of  these  acids  rrom  each  other  may  be 
effected  by  decomposing  their  persalts  of  iron  by  ammonia, 
and  treating  the  new-formed  compounds  with  alcohol, 
after  previous  evaporation  to  dryness.  The  separation  of 
these  acids  is,  of  course,  even  more  simple,  if  we  can 
combine  them  with  alkalies  in  a  more  direct  way.  The 
benzoate  in  that  case  dissolves,  whilst  the  succinate  remains. 

Third  Group  of  the  Organic  Acids. 

ACIDS   WHICH   ARE    NOT  PRECIPITATED,  UNDER    ANY  CONDI- 
TION,    BY    CHLORIDE     OF    CALCIUM     OR    PERCHLORIDE    OF 

IRON  :  Acetic  Acid,  Formic  Acid* 

§  104. 
a.  ACETIC  ACID.     (A=C4  H3  03.) 

1.  Acetic  acid  is  completely  volatilized  by  heat,  forming 
vapours  of  a  pungent  odour,  which  in  their  concentrated 
slate  are  inflammable  and  burn  with  a  blue  flame.     The 
acetates  are  decomposed  at  a  red  heat.     Among  the  pro- 
ducts of  their  decomposition  we  usually  find  acetic  acid, 
and  invariably  acetone.    The  acetates  which  have  an  alkali 
or  alkaline  earth  for  their  base  are  converted  into  carbon- 
ates, in  this  process.     Many  of  those  with  a  metallic  base 
leave  the  metal  behind  in  its  metallic  state,  others  as  oxide. 
All  the  residues  are  carbonaceous.     Almost  all  acetates 
are  soluble  in  water  and  alcohol ;  most  of  them  readily 
dissolve  in  water,  but  a  few  are  difficult  of  solution. 

2.  If  perchloride  of  iron  is  added  to  acetic  acid,  no 
alteration  takes  place,  but  if  the  acid  is  previously  satu- 
rated with  ammonia,  or  if  a  neutral  acetate  is  mixed  with 
perchloride  of  iron,  the  solution  assumes  a  deep  and  dark 
red  tint,  owing  to  the  formation  of  PERACETATE  OF  IRON. 
Ammonia  precipitates  all  the  peroxide  of  iron  from"  such 
a  solution. 

3.  Neutral  acetates  (but  not  free  acetic  acid)  yield  with 
nitrate  of  silver,  white  crystalline  precipitates  of  ACETATE 
OF  SILVER,  (Ag  O,  A)  which  are  very  sparingly  soluble  in 
cold  water.     They  dissolve  more  readily  in  hot  water,  but 
they  separate  again  from  the  solution,  on  cooling,  in  the 


FORMIC  ACID.  171 

form  of  very  fine  crystals.  Ammonia  dissolves  them 
readily ;  free  acetic  acid  does  not  increase  their  solubility 
in  water. 

4.  Protonitrate  of  mercury  produces  in  solutions  of 
acetic  acid,  and  even  with  greater  facility  in  solutions  of 
acetates,  white  scaly  crystalline  precipitates  of  PROTACE- 
TATE   OF   MERCURY,   (Hg3  O,  A,)   which   are   sparingly 
soluble  in  water  and  acetic  acid,  at  a  low  temperature,  but 
easily  soluble  in  an  excess  of  the  precipitant.     Protacetate 
of  mercury  dissolves  in  water  on  the  application  of  heat, 
but  separates  again,  on  cooling,  in  the  form  of  small  crys- 
tals ;  it  becomes  partly  decomposed  in  this  process,  me- 
tallic mercury  separates  and  imparts  a  gray  colour  to  the 
precipitate.     If  protonitrate    of  mercury  is   boiled   with 
dilute  acetic  acid  instead   of  water,  the  quantity  of  the 
metallic  mercury  separating  is  exceedingly  minute. 

5.  If  acetates   are  heated  with  dilute  sulphuric  acidj 
ACETIC  ACID  is  evolved,  which  may  be  detected  by  its  pun- 
gent odour.     And  if  the  acetates  are  heated  with  about 
equal  weights  of  concentrated  sulphuric  acid  and  alcohol, 
ACETIC  ETHER  is  evolved ;  the  odour  of  this  ether  is  highly 
characteristic  and  agreeable  ;  it  becomes  particularly  per- 
ceptible on  agitating  the  mixture  when  somewhat  cooled 
down,  and  scarcely  admits  of  any  mistake,  and  certainly 
far  less  than  the  pungent  odour  of  free  acetic  acid. 

6.  If  acetates  are  distilled  with  dilute  sulphuric  acid, 
and  the  distillate  digested  with  oxide  of  lead  in  excess, 
part  of  this  oxide  will  be  dissolved  as  a  basic  acetate  of 
lead,  which  may  easily  be  detected  by  its  alkaline  reaction. 

b.  FORMIC  ACID.     (Fo  O3  =  C2HO3.) 

1.  Formic  acid  has  a  characteristic  pungent  odour;  it 
volatilizes  completely  on  heating  ;  the  vapours  of  the  con- 
centrated acid  are  inflammable  and  burn  with  a  blue  flame. 
The  formiat.es,  like  the  corresponding  acetates,  when 
heated  to  redness,  leave  either  carbonates  or  oxides,  or 
metals  behind ;  with  simultaneous  separation  of  carbon, 
carburetted  hydrogen,  and  escape  of  carbonic  acid  and  of 
water.  All  combinations  of  formic  acid  with  bases  are 
soluble  in  water  ;  alcohol  does  not  dissolve  all  of  them. 


172  FORMIC  ACID- 

2.  Formic  acid  presents  the  same  relation  to  perchloride 
of  iron  as  acetic  acid. 

3.  Nitrate  of  silver  does  not  precipitate  free  formic  acid, 
and  precipitates  alkaline  formiates  only  from  concentrated 
solution.     The  white,    sparingly  soluble,  crystalline  pre- 
cipitate of  FORMIATE  OP  SILVER  (Fo  O-{  AgO)  soon  assumes 
a  deeper  tint  owing  to  the  separation  of  metallic  silver. 
This  reduction  to  metallic  silver  takes  place,  even  at  a  low 
temperature,  after  the  solution  containing  the  formiate  of 
silver  has  been  allowed  to  stand  for  some  time,  but  it  fol- 
lows instantaneously  upon  the  fluid  being  heated  with  the 
precipitate.     The  same  reduction  of  the  oxide  of  silver 
ensues  even  if  the  solution  of  the  formate  was  so  dilute, 
that  no  precipitate  had  been  formed,  or  if  we  have  to  ope- 
rate upon  free  formic  acid.     In  this  process,  the  formic 
acid,  which  may  be  considered  a  compound  of  carbonic 
oxide  and  water,  deprives  the  oxide  of  silver  of  its  oxygen, 
giving  rise  to  the  formation  of  carbonic  acid,  which  escapes, 
and  of  water ;  the  metal  is  precipitated  in  its  metallic  state. 

4.  Protonitrate  of  mercury  does  not  produce  precipita- 
tion in  free  formic  acid  ;  but  in  concentrated  solutions  of 
alkaline    formiates   it   causes   a  white,  sparingly  soluble 
precipitate  of  PROTOFORMIATE   OF  MERCURY, '(Fo  O3  Hg3 
O,)  which  after  a  very  short  time  turns  gray,  owing  to  the 
separation  of  metallic  mercury  ;  complete  reduction  takes 
place,  sometimes  even  at  a  low  temperature,  but  instanta- 
neously on  heating.     In  this  process,  also,  carbonic  acid 
and  water   are   formed.      This   reduction,   in  the   same 
manner,  as  is  the  case  with  the  nitrate  of  silver,  takes 
place,  even  if  the  fluid  is  so  dilute,  that  the  protoformiate 
of  mercury  remains  in  solution,  or  if  we  have  free  formic 
acid  to  operate  upon. 

5.  If  formic  acid  or  an  alkaline  formiate  be  heated  with 
perchloride  of  mercury  to  60-70°  Reaumur,*a  precipitate 
of  PROTOCHLORIDE  OF  MERCURY  is  obtained.    When  heated 
to  the  boiling  point  of  water,  metallic  mercury  separates 
besides  the  protochloride. 

6.  If  formic  acid  or  a  formiate  is  heated  with  concen- 
trated sulphuric   acid,   it  becomes    decomposed  without 
blackening  the  fluid,  giving  rise  to  the  formation  of  water 
and  carbonic  oxide  gas,  which  escapes  with  effervesence, 


FORMIC  ACID.  173 

and  when  ignited,  burns  with  a  blue  flame,  The  sulphuric 
acid  withdraws  from  the  formic  acid,  the  water  or  oxide 
necessary  to  the  existence  of  this  substance,  and  thus 
causes  a  transposition  of  mits  atoms  to  take  place  (C2 
H  O3=  2  CO-I-HO.)  If  a  formiate  is  heated  with  dilute 
nitric  acid,  formic  acid  escapes,  which  may  easily  be 
detected  by  its  odour.  If  a  formiate  is  drenched  with  a 
mixture  of  sulphuric  acid  and  alcohol,  formic  fither  is- 
evolved,  which  is  characterized  by  its  peculiar  arraek 
smell. 

Recapitulation  andremarks. — As  the  reactions  of  acetic 
acid  and  formic  acid  are  not  so  characteristic  as  those  of 
many  other  acids,  their  safe  detection  can  only  be  based 
on  the  concurrence  of  all  the  reactions  we  have  stated. 
Acetic  acid  is  most  easily  detected  by  its  odour  or  by  that 
of  acetic  ether,  but  most  safely  by  its  behaviour  with  oxide 
of  lead.  Formic  acid  may  best  be-  detected  by  its  beha- 
viour with  sulphuric  acid  and  with  the  salts  of  the  noble 
metals.  The  separation  of  acetic  acid  from  formic  acid  is 
effected  by  heating  both  acids  with  peroxide  of  mercury  in 
excess,  or  with  oxide  of  silver.  The  formic  acid  reduces 
the  oxides,  and  becomes  decomposed  at  the  same  time  ; 
the  acetic  acid  combines  with  them  and  remains  in  solution. 


' 


PART   II. 


SYSTEMATIC    COURSE 


OF 


QUALITATIVE    CHEMICAL    ANALYSIS. 


PART  II, 
PRELIMINARY  REMARKS 

ON    THE 

COURSE  OF  QUALITATIVE  ANALYSIS  IN  GENERAL, 

AND    ON    THE 

PLAN  OF  THIS  SECOND  PART  OF  THE  PRESENT  WORK 

IN  PARTICULAR. 

WHEN  we  are  once  acquainted  with  the  reagents  and 
the  relation  of  other  bodies  to  them,  we  are  immediately 
able  to  determine,  whether  some  simple  compound  or 
other,  the  physical  qualities  of  which  admit  of  drawing  an 
inference  as  to  its  nature,  is  in  reality  what  we  take  it  to 
be.  Thus,  for  instance,  a  few  simple  reactions  convince 
us  that  a  body  which  we  suppose  to  be  calcareous  spar,  is 
really  carbonate  of  lime  ;  and  another  substance,  which  we 
deem  gypsum,  is  really  sulphate  of  lime.  This  know- 
ledge is  usually  equally  sufficient  to  ascertain,  whether  a 
certain  body  be  present  or  not  in  some  compound  sub- 
stance or  other ;  for  instance,  whether  a  white  powder 
contains  protochloride  of  mercury  or  not.  But  if  our  de- 
sign is  to  ascertain  the  chemical  nature  of  a  substance  en- 
tirely unknown  to  us — if  we  wish  to  discover  all  the  con- 
stituents of  a  mixture  or  a  chemical  combination — if  we 
intend  to  prove  that)  besides  certain  bodies  we  have  de- 
tected in  a  mixture  or  compound,  no  other  substance  can 
be  present  with  it,  and,  consequently,  if  a  COMPLETE  quali- 
tative analyses  our  object,  the  mere  knowledge  of  rea- 
gents and  reactions  is  no  longer  sufficient ;  we  must  of  ne^ 
cessity  know  besides  how  to  proceed  systematically  in  our 
analysis ;  i.  e.  we  must  know  in  what  order  we  have  to 


178  PRELIMINARY    REMARKS. 

apply  solvents,  and  general  and  especial  reagents,  so  as  to 
be  enabled  with  celerity  and  certainty  to  determine  that 
all  those  substances  which  a  compound  or  mixture  does 
NOT  contain,  ARE  REALLY  NOT  contained  in  it ;  and  on  the 
other  hand,  quickly  and  safely  to  detect  those  bodies  which 
ARE  PRESENT  in  the  substance  under  examination.  If  we 
do  not  possess  the  knowledge  of  this  systematic  course, 
or  if,  in  the  hope  of  more  rapidly  attaining  our  object,  we 
adhere  to  no  method  whatever  in  our  investigations  and 
experiments,  analysis  becomes  (at  least  in  the  hand  of  a 
novice)  mere  guessing,  and  the  results  obtained  are  110 
longer  the  fruits  of  scientific  calculation,  but  mere  matters 
of  accident,  which  sometimes  may  prove  lucky  hits,  and  at 
others  total  failures. 

A  definite  method,  therefore,  must  form  the  basis  of 
every  analytical  investigation.  But  it  is  not  by  any  means 
necessary  that  this  method  should  be  in  all  cases  one  and 
the  same.  Practice,  reflection,  and  a  due  attention  to  cir- 
cumstances, will,  on  the  contrary,  in  most  cases  direct  us 
to  various  and  different  methods.  But  all  analytical  me- 
thods agree  in  this,  that  the  substances  existing,  or  sup- 
posed to  exist,  must  first  be  divided  info  certain  groups, 
and  the  bodies  belonging  to  these  groups  be  further  dis- 
tinguished from  each  other,  so  as  at  last  to  admit  of  their 
individual  detection.  The  diversity  of  analytical  methods 
depends  partly  on  the  order  in  which  reagents  are  applied, 
and  partly  on  their  selection. 

Before  we  can  venture  upon  inventing  methods  of  our 
own  for  individual  cases,  we  must  first  make  ourselves 
thoroughly  conversant  with  a  certain  definite  course  or 
system  of  chemical  analysis  in  general.  This  system 
must  have  passed  through  the  ordeal  of  experience,  and 
must  be  adapted  to  every  case  imaginable,  so  as  to  enable 
us  afterwards,  when  we  have  acquired  some  practice  in 
analysis,  to  determine  which  modification  of  ttie  general 
method  will,  in  certain  given  cases,  most  easily  and  rapidly 
lead  to  the  attainment  of  the  object  in  view. 

The  exposition  of  such  a  systematic  couise,  adapted  to 
all  cases,  tested  by  experience,  and  combining  the  greatest 
possible  simplicity  with  the  greatest  possible  security,  is 
the  object  of  the  second  part  of  this  work. 


PRELIMINARY  REMARKS.  179 

The  elements  and  combinations  comprised  in  it  are  the 
same  which  we  have  enumerated  in  our  preliminary 
remarks. 

Since  it  is  necessary  in  the  formation  of  such  a  system- 
atic course  to  provide  for  every  possible  circumstance  which 
may  occur,  it  follows,  as  a  matter  of  course,  that  we  are 
obliged  to  suppose  those  substances  which  we  treat  of — 
(however  mixed  and  intermixed  with  each  other  we  may 
admit  them  to  be)  free  from  extraneous  organic  matters, 
since  the  presence  of  such  matters  prevents  the  manifesta- 
tion of  many  reactions,  and  causes  various  modifications  in 
others.  We  by  no  means  intend  to  assert  here  that  the 
proposed  systematic  course  may  not  be  exactly  followed 
even  in  presence  of  many  organic  substances,  especially  of 
those  which  dissolve  in  water,  forming  colourless  transpa- 
rent fluids.  Experience  and  reflection  in  every  individual 
case  will  best  instruct  us  how  to  act  in  cases  where  dark 
colouring  slimy  matters  are  present.  For  the  most  impor- 
tant rules,  and  the  method  in  general,  we  refer  to  §  129. 

This  second  part  is  divided  into  two  sections  ;  the  first 
contains  PRACTICAL  INSTRUCTIONS  IN  ANALYSIS,  wherein 
we  have  pointed  out  a  way  which  must  lead  to  the  end  in 
view,  if  systematically  followed.  At  first  sight,  many  parts 
of  it  may,  perhaps,  be  deemed  rather  prolix  ;  I  think,  howe- 
ver, that  it  would  have  scarcely  been  possible  to  abbreviate 
it,  except  at  the  expense  of  clearness  and  perspicuity  for 
beginners.  I  hope,  moreover,  that  my  readers  will  soon 
become  convinced  by  experience  that  this  prolixity,  after  all, 
does  not  prove  any  bar  to  the  celerity  with  which  the  sys- 
tematic course  may  be  gone  through,  as  I  have  always 
divided  the  phenomena  which  may  occur,  into  clearly  cha- 
racterized instances;  and  thus  a  given  object  being  the  only 
one  to  be  considered,  and  one  number  always  referring  to 
the  other,  the  student  may  save  himself  the  trouble  of  read- 
ing through  those  parts  which  are  not  adapted  for  the 
especial  case  engaging  his  attention. 

The  subdivisions  of  this  practical  course  are,  1 ,  Preli- 
minary examination  ;  2,  Solution  ;  3,  Real  examination  ; 
4,  Confirmatory  experiments.  The  third  subdivision  (the 
real  examination)  is  again  subdivided  into,  1,  Examination 
of  compounds  in  which  we  suppose  but  one  basis  and  but 


180  PRELIMINARY    REMARKS. 

one  acid  present;  and,  2,  Examination  of  mixtures  or  com- 
pounds in  which  we  suppose  that  all  those  substances 
which  we  have  taken  into  consideration  may  be  present. 
With  respect  to  the  latter,  it  must  be  observed  that  where 
the  preliminary  examination  has  not  afforded  us  the  most 
certain  conviction  of  the  absence  of  certain  groups  of  sub- 
stances, we  cannot  safely  disregard  any  paragraph  to  which 
we  refer,  in  consequence  of  the  phenomena  that  manifest 
themselves.  In  cases  where  we  merely  intend  to  test  a 
combination  or  mixture  for  certain  substances,  and  not  for 
all  its  constituents,  it  will  be  easy  to  find  those  numbers 
which  we  have  to  take  into  consideration. 

The  second  section  contains  an  EXPLANATION  OF  THE 
PRACTICAL  PROCESS,  an  exposition  and  explanation  of  the 
grounds  whereon  the  separation,  and  the  causes,  whereon 
the  detection  of  substances  depend ;  and,  moreover,  various 
additions  to  the  first  section.  Students  would  do  well  to 
make  themselves  early  acquainted  with  this  section,  which 
may  be  advantageously  studied,  concurrently  with  the 
practical  process. 

As  an  appendix,  we  give  A  GENERAL  SCHEME  OF  THE 

ORDER  IN  WHICH  THOSE  SUBSTANCES  WHICH  ARE  TO  BE 
ANALYZED  FOR  THE  SAKE  OF  PRACTICE  MAY  MOST  JUDI- 
CIOUSLY BE  SUCCESSIVELY  TAKEN;  and  ALSO  A  TABULAR 
ARRANGEMENT  OF  THE  MORE  FREQUENTLY  OCCURRING 
FORMS  AND  COMBINATIONS  OF  THE  SUBSTANCES  ENUME- 
RATED IN  OUR  PRELIMINARY  REMARKS,  ACCORDING  TO 
THEIR  VARIOUS  DEGREES  OF  SOLUBILITY  IN  WATER  AND 

ACIDS.  The  first  is  intended  to  serve  the  pupil  as  a  guide 
to  the  rapid  and  certain  attainment  of  his  object ;  i.  e.  a 
sound  and  complete  acquisition  of  qualitative  analysis;  and 
the  second  will,  undoubtedly,  prove  useful  to  many  who  are 
not  yet  quite  conversant  with  the  various  degrees  of  solu- 
bility of  compound  bodies,  especially  in  cases  where  they 
have  to  draw  conclusions  as  to  how  the  detected  acids, 
bases,  &c.,  have  been  combined,  or  what  particular  acids 
cannot  possibly  be  present  in  aqueous  or  acid  solutions, 
when  the  latter  contain  certain  bases. 


' 


PRELIMINARY   EXAMINATION.  181 

FIRST  SECTION. 
PRACTICAL  PROCESS. 

I.   PRELIMINARY    EXAMINATION. 

§   105. 

In  the  first  place,  the  external  and  sensible  properties 
of  the  substance  under  examination  should  be  considered, 
such  as  its  colour,  shape,  hardness,  gravity,  odour,  &c.,  as 
many  conclusions  may  often  be  drawn  therefrom.  Before 
proceeding  any  further,  we  ought  to  consider  well  how 
much  of  the  substance  to  be  examined  we  have  at  com- 
mand, since  it  is  necessary  at  this  early  period  of  the  exa- 
mination to  determine  the  quantity  which  we  may  use  in 
the  preliminary  investigation.  A  reasonable  economy  is 
in  all  cases  advisable,  though  we  may  possess  the  sub- 
stance in  large  quantities  ;  and  it  must  be  laid  down  as  a 
fixed  rule,  never  to  use  at  once  all  we  possess  of  a  sub- 
stance, but  always  to  keep  at  least  a  small  portion  of  it 
for  unforeseen  accidents,  and  for  confirmatory  experi- 
ments. 

A.  THE  BODY  UNDER  EXAMINATION  IS  SOLID. 

»  I.    IT  IS  NEITHER  A  PURE  METAL    NOR  AN  ALLOY. 

1.  The  substance  is  fit  for  examination  when  in  powder 
or  in  small  crystals ;  but  when  in  larger  crystals  or  in 
solid  pieces,  a  -portion  of  it,  if  possible,  must  first  be  re- 
duced to  powder. 

2.  The  powder  is  heated  over  the  spirit-lamp,  in  a  small 
iron  spoon.     The   phenomena  resulting   admit  of  many 
safe  inferences  as  to  the  nature  of  the  substance,  and  allow 
us  to  draw  many  probable  conclusions. 

a.  THE  SUBSTANCE  REMAINS  UNALTERED  :  no  or- 
ganic substances,  no  salts  containing  water  of  crys- 
tallization, no  easily  fusible  matter,  no  volatile  bodies. 

b.  IT    FUSES     EASILY,    AND    BECOMES     SOLID    AGAIN 
WITH     THE     EXPULSION     OF     AQUEOUS     VAPOUR  J    Salts 

which  contain  water  of  crystallization.     If  the  solidi- 

8 


182  PRELIMINARY    EXAMINATION. 

fied  residue  fuses  again  upon  the  application  of  an 
increased  heat,  c  must  be  referred  to. 

;\  C.  IT  FUSES  WITHOUT  EXPULSION  OF  AQUEOUS  VA- 
POUR. A  small  piece  of  paper  is  added  to  the  melt- 
in,/  mass ;  if  deflagration  lakes  place,  it  indicates 
NITRATES,  or  more  rarely,  CHLORATES. 

d.    IT    VOLATILIZES    COMPLETELY    OR    PARTLY.       In 

the  first  case,  no  fixed  bases  are  present ;  in  the  latter, 
the  substance  contains  a  volatile  body  in  admixture. 

a.  No  odour  is  emitted.  In  this  case  we  must 
especially  have  regard  to  compounds  of  AMMONIA, 
MERCURY,  and  ARSENIC. 

j8.  An  odour  is  emitted  at  the  same  time.     If  it 
is  that  of  sulphurous  acid,  SULPHUR  is  present ;  if 
that  of  iodine,  and  if  the  vapours   arc  violet,  the 
presence  of  free  IODINE  is  certain.     With  equal  cer- 
tainty free  BENZOIC  ACID,  and  many  other  substances, 
may  be  detected  by  the  odourfof  their  vapours. 
e.  THE  SUBSTANCE  is  A  WH|TE  POWDER  TURNING 
TO  .YELLOW  ON   HEATING  ]  this    indicates  OXIDE  OF 
ZINC  or  OXIDE  OF  LEAD  }  the  latter  substance  remains 
yellow  on  cooling,  whilst  the  oxide  of  zinc  resumes 
its  white  colour. 

/.  CARBONIZATION  TAKES  PLACE  :  organic  sub- 
stances. If  the  residue  effervesces  when  drenched 
with  acids,  whilst  the  original  substance  does  not 
present  that  property,  it  indicates  the  presence  of 
ORGANIC  ACIDS,  comb.iiicd  with  alkalies  or  alkaline 
matter.  If  the  odour  of  cyanogen  is  perceptible,  it 
indicates  the  presence  of  a  CYANIDE.  . 

Many  substances,  moreover,  swell  up  considerably, 
as  for  instance,  borax,  sulphate  of  alumina ;  others 
decrepitate,  e.  g.  chloride  of  sodium,  and  chloride  of 
potassium,  &c. ;  these  phenomena,  however,  less 
admit  of  general  and  certain  conclusions  than  those 
stated  above. 

|VK  3.  A  small  portion  of  the  substance  is  put  on  a  charcoal 
support,  and  exposed  to  the  reducing  flame  of  the  blow- 
pipe. Since  most  of  the  phenomena  just  now  described 
(2)  are  equally  obtained  by  this  process,  we  will  here 
mention  only  those  which  particularly  belong  to  the  latter. 


BY    HEAT.      THE    BLOW    PIPE.  183 

a.  THE  SUBSTANCE  VOLATILIZES  PARTLY  OR  COM- 
PLETELY.    This    indicates    besides    the   substances 
mentioned  in  §  105,  2,  d,  also  OXIDE  OF  ANTIMONY, 
and  several  other  oxides.      (Compare  §  105,  6,  d,  /3.) 
Oxide  of  antimony  fuses  previous  to  its  volatilization, 
in  the  form  of  a  white  vapour.  It  must,  moreover,  be 
remarked,  that  when  ARSENIOUS  or  ARSENIC  ACID  are 
present,  a  characteristic  odour  of  garlic  is  perceptible, 
which  is  stronger  if  soda  has  previously  been  added 
to  the  test  specimen. 

b.  TlIE     BODY     FUSES,    AND     IS     IMBIBED     BY    THE 

CHARCOAL  ;  this  indicates  the  presence  of.  ALKALIES. 
This  process  is  conducted  by  putting  a  portion  of  the 
substance  reduced  to  powder  on  the  moistened  loop 
of  a  platinum  wire,  and  applying  the  heat  of  the  re- 
ducing blow-pipe  flame  to  it.  If  the  oxidizing  flame 
assumes  a  violet  tint,  it  indicates  the  presence  of  POT- 
ASH alone  ;  if  a  yellow  tint,  the  presence  of  SODA, 
which  may,  however,  be  mixed  with  potash,  even  in 
a  considerable  proportion,  since  the  flame  always  ap- 
pears yellow  when  both  these  alkalies  are  present. 

C.  AN  INFUSIBLE  WHITE  RESIDUE  REMAINS  ON  THE 
CHARCOAL,  EITHER  IMMEDIATELY,  OR  AFTER  .PREVIOUS 
MELTING  IN  THE  WATER  OF  CRYSTALLIZATION  ]  this 

indicates  especially  the  presence  of  barytes/strontian, 
lime,  magnesia,  alumina,  zinc,  and  silicic  acid.  Of 
these  substances  STRONTIAN,  LIME,  MAGNESIA,  and 
ZINC,  are  distinguished  by  being  very  luminous  in  the 
blow  pipe  flame.  A  drop  of  solution  of  nitrate  of 
cobalt  is  added  to  the  white  residue,  and  the  latter 
then  again  strongly  heated.  ALUMINA  presents  a  fine 
blue  tint,  MAGNESIA  a  reddish,  and  ZINC  a  green 
colour.  When  SILICIC  ACID  is  present,  the  flame  as- 
sumes also  a  feeble  bluish  tint,  which  should  not  be 
confounded  with  that  produced  by  alumina.  Silicic 
acid  is  moreover  distinguished  by  forming  a  clear 
glass,  with  effervescence,  when  mixed  with  carbonate 
of  soda,  and  exposed  to  a  strong  blow-pipe  flame. 
(§  99,  b.) 

d.  AN  INFUSIBLE  RESIDUE  OF  A  DIFFERENT  CO- 
LOUR REMAINS,  OR  A  METALLIC  REDUCTION  TAKES 


184  PRELIMINARY    EXAMINATION.  £1 

PLACE,    WITH    OR     WITHOUT     INCRUSTATION     OF    THE 

CHARCOAL  SUPPORT.  A  portion  of  the  powder  is 
mixed  with  carbonate  of  soda,  and  heated  in  the  re- 
ducing flame  on  charcoal. 

«.  A  metallic  grain  is  obtained,  without  simulta- 
neous incrustation  of  the  charcoal ;  this  indicates 
the  presence  of  GOLD,  SILVER,  TIN,  OR  COPPER. 
Platinum,  iron,  cobalt,  and  nickel,  equally  become 
reduced,  but  yield  no  metallic  grains. 

/3.  The  charcoal  support  is  coated  over  with  an 
incrustation,  either  with  or  without  simultaneous 
formation  of  a  metallic  grain :  this  indicates  the 
presence  of  bismuth,  lead,  cadmium,  antimony,  or 
zinc. 

aa.  If  the  incrustation  is  white,  ANTIMONY 
or  ZINC  may  be  supposed  present.  The  in- 
crustation produced  by  zinc  appears  yellow  as 
long  as  it  remains  hot.  The  pure  metallic 
grain  of  antimony  evolves  white  vapour,  even  for 
a  long  time  after  all  application  of  heat  has  been 
withdrawn ;  and  at  last,  on  cooling,  becomes 
generally  surrounded  with  crystals  of  oxide  of 
antimony.  It  is  brittle  under  the  stroke  of  a 
hammer. 

bb.  The  incrustation  is  more  or  less  yellow 
or  brown  ;  this  indicates  the  presence  of  BISMUTH, 
LEAD,  or  CADMIUM.  The  yellow  incrustation  of 
oxide  of  cadmium  has  a  shade  of  orange  colour 
in."  it;  the  brownish-yellow  incrustations  of  oxide 
of  lead  and  oxides  of  bismuth  change  into  a  light 
yellow  on  cooling.  Cadmium  immediately  volati- 
lizes on  becoming  reduced.  The  grains  of  lead 
are  very  ductile,  whilst  the  grains  of  bismuth 
are  brittle  under  the  stroke  of  the  hammer. 

The  student  must  be  prepared,  of  course,  to  meet  with 
combinations  of  bodies  giving  rise  to  mixed  phenomena, 
and  must  deduce  his  conclusions  accordingly,  since  we 
cannot  give  strictly  denned  cases  in  these  general  rules. 


OF  METALS  AND  ALLOYS.  185 

II.  THE  SUBSTANCE  IS  A  METAL  OR  AN  ALLOY. 

1 .  The  test-specimen  is  drenched  and  heated  with  water, 
mixed  with  some  acetic  acid. 

a.  HYDROGEN  is  EVOLVED  ;  this  indicates  the  pre- 
sence of  a  light  metal.     The  presence  of  alkalies  and 
of  alkaline  earths  must  be  had  regard  to  in  the  real 
examination. 

6.  No  HYDROGEN  is  EVOLVED  ;  this  indicates  the 
absence  of  light  metals.  Alkalies  and  alkaline  earths 
need  not  be  considered  in  the  course  of  the  special 
investigation. 

2.  The  test-specimen  is  heated  on  charcoal,  in  the  redu- 
cing blow-pipe  flame,  and  the  phenomena  observed,  such 
as,   for   instance,  whether  the    substance  fuses,  whether 
an  incrustation  is  formed,   whether  any  odour  is  emit- 
ted, &c. 

a.  THE  SUBSTANCE  REMAINS  UNALTERED  ;  this  is 
pretty  conclusive  of  the  absence  of  antimony,  zinc, 
lead,  bismuth,  cadmium,  tin,  mercury,  and  arsenic ; 
the  absence  of  gold,  silver,  and  copper,  is  also  proba- 
ble ;  it  indicates  the  presence  of  PLATINUM,  IRON, 

MANGANESE,  NIKEL,  Or   COBALT. 

b.  THE  SUBSTANCE   FUSES  WITHOUT  SIMULTANEOUS 
INCRUSTATION,     AND    WITHOUT  EMISSION     OF     ODOUR  J 

this  indicates  the  absence  of  antimony,  zinc,  lead,  bis- 
muth, cadmium,  and  arsenic,  and  the  presence  of  GOLD, 

SILVER,  COPPER,   Or   TIN. 

C.    THE   SUBSTANCE  FUSES  WITH  THE  FORMATION  OF 
A  CRUST,    BUT     WITHOUT    EMITTING    ANY  ODOUR  ',     this 

indicates  the  absence  of  arsenic,  and  the  presence  of 

ANTIMONY,  ZINC,  BISMUTH,  LEAD,  Or  CADMIUM.      (Com- 

pare  §  105  A.  I.,  3  d,  ft.) 

d.    THE  SUBSTANCE  EMITS  A  GARLIC  ODOUR  }    this  Ul- 

dicates  the  presence  of  ARSENIC.  For  the  other  phe- 
nomena which  may  manifest  themselves,  we  refer  to 
a.  6,  or  c. 

3.  The  substance  is  heated  before  the  blow-pipe  in  a 
glass  tube,  closed  at  one  end. 

a.  No  SUBLIMATE  IS  FORMED  IN  THE  COLDER  PART 

OF  THE  TUBE  ;  this  indicates  the  absence  of  mercury. 

b.  A  SUBLIMATE  is  FORMED  ;  this  indicates  the  pr e- 


186  PRELIMINARY  EXAMINATION. 

sence  of  MERCURY,  CADMIUM,  or  ARSENIC.  The  sub- 
limate of  mercury,  which  consists  of  small  globules, 
cannot  be  confounded  with  the  sublimate  of  cadmium 
or  arsenic. 

B.    THE  SUBSTANCE  UNDER  EXAMINATION  IS  A  FLUID. 

1 .  A  small  portion  of  the  fluid  is  evaporated  in  a  plati- 
num spoon,  or  in  a  small  porcelain  crucible,  to  enable  us 
to  determine  whether  the  fluid  contains  any  substance    in 
solution,  and  what  is  the  nature  of  the  residue.     (§  105 
A.) 

2.  The  fluid  is  tested  by  litmus  papers. 

a.  BLUE  LITMUS  PAPER  BECOMES  RED.     This  reac- 
tion may  be  caused  either  by  a  free  acid,  or  an  acid 
salt,  or  by  a  soluble  metallic  salt.     In  order  to  distin- 
guish these  two  cases  from  each  other,  a  small  quanti- 
ty of -the  liquid  is.  poured  into  a  watch-glass,  and  a  lit- 
tle rod  placed  into  it,  the  extreme  point  of  which  has 
previously  been  dipped  into  dilute  solution  of  carbo- 
nate  of  potash;  if  the  fluid  remains  clear,  or  if  the 
precipitate  which  may  form  is  redissolved  on  stirring 
the  liquid,  it  indicates  the  presence  of  a  free  acid  or 
an  acid  salt ;  but  if  the  fluid  becomes  turbid,  it  proves 
the  presence  of  a  soluble  metallic  salt,  at  least  gene- 
rally.    As  a  matter  of  course,  with  the  presence  of  a 
free  acid  or  acid  salt,  the  solution  cannot  be  considered 
as  a  mere  aqueous  one,  and  consequently  we  must  look 
carefully  to  all  those  phenomena  which  may  indicate 
the  presence  of  bodies  insoluble  in  water,  and  soluble 

.    only  in  acids. 

b.  REDDENED  LITMUS  PAPER  BECOMES  BLUE  ;  this 
indicates  the  presence  of  free  alkalies,  or  alkaline 
carbonates,  free  alkaline  earths,  or  alkaline  sulphu- 
rets,  and  also  of  a  series  of  other  salts  of  which  this 
reaction  is   characteristic.     With  the  presence  of  a 
free  alkali,  a  body  dissolved  in  the  fluid  may  as  well 
belong  to  those  soluble  as  to  those  insoluble  in  water. 
We  refer  to  §  114  I.,  2,  for  further  information  on 
this  subject. 

3.  We  test  by  smelling  and  tasting,  or  should  this  n^t 
yield  any  safe  results,  by  distillation,  whether  the  simple 


CLASSIFICATION  OF  SUBSTANCES.  187 

solvent  present  is  water,  alcohol,  ether,  &c.  If  it  is  found 
not  to  be  water,  the  solution  is  evaporated  to  dryness,  and 
the  residue  treated  according  to  §  106  A. 

4.  If  the  solution  is  aqueous,  and  manifests  an  acid 
reaction,  a  portion  of  it  is  highly  diluted:  with  water.  If 
it  becomes  milky,  the  presence  of  ANTIMONY,  BISMUTH,  or 
TIN,  may  be  supposed.  If  the  precipitate  disappears  on 
the  addition  of  tartaric  acid,  we  may  conclude  that  anti- 
mony is  present,  whilst  its  disappearance  on  the  addition 
of  acetic  acid,  but  not  of  tartaric  acid,  indicates  the  pre- 
sence of  bismuth.  The  original  fluid  is  then  treated  either 
as  §  107  directs,  or  §  114,  according  to  whether  we  have 
reason  to  suppose  it  to  be  the  solution  of  a  simple  or  of  a 
compound  or  mixed  substance. 

II.  SOLUTION  OF  BODIES  OR  CLASSIFICATION  OF  SUB- 
STANCES ACCORDING  TO  THEIR  RELATIONS  TO  CERTAIN 
SOLVENTS. 

§   106. 

Water  and  hydrochloric  acid,  or  in  certain  cases  acetic 
acid,  are  the  solvents  used  to  classify  simple  or  compound 
substances,  and  to  isolate  the  component  parts  of  mixtures. 
We  divide .  substances  into  three  classes,  according  to 
their  relations  to  these  solvents. 

First  class, — SUBSTANCES  SOLUBLE  IN  WATER. 
Second  class. — SUBSTANCES  INSOLUBLE  OR  SPAR- 
INGLY   SOLUBLE    IN    WATER,  BUT  SOLUBLE    IN    HYDRO- 
CHLORIC OR  NITRIC    ACID. 

Third  class. — SUBSTANCES  INSOLUBLE  OR  SPAR- 
INGLY SOLUBLE,  BOTH  IN  WATER,  AND  ALSO  IN  HYDRO- 
CHLORIC OR  IN  NITRIC  ACID. 

A  special  method  for  the  solution  of  alloys  is  given  in 
§  106  B,  as  it  is  advisable  to  dissolve  them  in  a  manner 
somewhat  different  from  that  employed  by  other  bodies. 

The  process  of  solution  or  separation  is  conducted  in 
the  following  manner. 

A.    THE  SUBSTANCE  UNDER  EXAMINATION  IS  NEITHER  A  METAL 
NOR  AN  ALLOY. 

1.  About  fifteen  or  twenty  grains  of  the  substance  to 


188  SOLUTION    AND    SEPARATION. 

be  examined,  reduced  to  powder,  are  covered  in  a  test- 
tube  with  ten  or  twelve  times  as  much  water,  and  heated 
to  the  boiling  point  over  a  spirit-lamp. 

a.  THE  SUBSTANCE  is  COMPLETELY  DISSOLVED.     In 
this  case  it  belongs  to  the  first  class  ;  regard  must  be 
had  to  what  we  have  stated  in  §  105  B,  2,  concerning 
reactions.     The  solution   is  treated  either  as  stated 
at  §  107,  and  at  §  114,  according  as  to  whether  one 
or  several  acids  and  bases  are  supposed  to  be  present. 

b.  A  RESIDUE   REMAINS,  EVEN  AFTER  BOILING    THE 

SOLUTION  FOR  A  LONG  TIME.  The  solution  is  allowed 
to  settle,  and  filtered,  so  that  the  residue  remains  in 
the  test-tube  if  possible  ;  a  few  drops  of  the  clear 
filtrate  are  then  evaporated  on  a  clean  platinum  plate  ; 
if  no  residue  remains,  the  substance  is  completely 
insoluble  in  water,  and  is  then  further  tested,  as  stated 
in  §  106,  2.  But  if  a  residue  remains,  the  substance 
is  at  least  partly  soluble.  It  is  then  again  boiled  with 
water,  filtered,  and  the  filtrate  added  to  the  original 
solution.  This  fluid  is  treated,  according  to  circum- 
stances, either  as  §  107  directs,  or  as  stated  §  114. 
The  residue  is  washed,  and  treated  according  to 
§  106,  2. 

2.  This  residue  is  drenched  with  dilute  hydrochloric 
acid.  If  it  does  not  dissolve,  it  is  heated  to  the  boiling 
point,  and  if  even  then  no  complete  solution  lakes  place, 
the  fluid  is  decanted,  and  the  residue  boiled  with  concen- 
trated hydrochloric  acid. 

The  phenomena  which  may  manifest  themselves 
in  this  operation,  and  which  ought  to  be  carefully 
observed,  are,  *,  Effervescence,  which  indicates  the 
presence  of  carbonic  acid,  or  sulphuretted  hydrogen, 
vide  §  108,  2.  P>.  Evolution  of  chlorine,  which  indi- 
cates the  presence  of  hyperoxides.  chromates,  &c. 
•y.  Emission  of  the  odour  of  hydrocyanic  acid,  which 
indicates  the  presence  of  insoluble  cyanides.  Since 
it  is  advisable  to  decompose  the  latter  in  a  different 
manner,  a  special  paragraph  will  be  devoted  to  them. 
(Vide  §  128.) 

a.  The  RESIDUE  is  COMPLETELY  DTSSOLVED  BY  THE 
HYDROCHLORIC  ACID  ;  the  solution  is  treated  accord- 


SOLUTION  AND  SEPARATION.  189 

ing  to  circumstances,  either  as  directed  §  110,  or  as 
stated  §  114.  The  substance  belongs  to  the  second 
class* 

The  separation  of  undissolved  sulphur,  which  is 
easily  detected  by  its  colour  and  specific  gravity, 
belong  also  to  this  category. 

b.  A  RESIDUE  REMAINS.  In  this  case  the  test-tube 
containing  the  specimen  boiled  with  hydrochloric 
acid,  is  put  aside  pro  tempore,  and  another  specimen 
of  the  substance  under  examination  is  boiled  with 
nitric  acid,  with  the  subsequent  addition  of  water. 

<*,  The  specimen  is  completely  dissolved,  or 
undissolved  sulphur  alone  remains  ;  the  body  in 
these  cases  also  belongs  to  the  second  class ; 
the  solution  is  further  tested  for  bases,  according 
to  circumstances,  either  as  directed  $  110,  or  as 
stated  §  114,  iii. 

/3.  A  residue  remains. 

aa.  WE  HAVE  REASON  TO  SUPPOSE  THAT  THE 

SUBSTANCE    UNDER  EXAMINATION    CONTAINS  BUT 

ONE  BASE  AND  ONE  ACID.  The  substance  is 
drenched  with  aqua  regia,  and  then  heated. 

«*.      The  substance  dissolves.     The  solu- 
tion is  treated  according  to  §  1 10. 

££.   The  substance  does  not  dissolve.     In 
that  case  we  proceed  according  to  §  113. 

bb.  WE  HAVE  REASON  TO  SUPPOSE  THAT  THE 
SUBSTANCE  UNDER  EXAMINATION  IS  A  COMBINA- 
TION OR  MIXTURE  OF  SEVERAL  COMPOUNDS.  Inthis 

case  the  reserved  hydrochloric  solution  (§  106  A. 
2,  &,)  is  used  to  test  for  the  bases.  It  is  for  this 
purpose  heated  to  boiling  with  the  insoluble 
residue — (which  latter  must  then  be  treated  as 
stated,  §  106,  3) — and  filtered  hot  into  a  tube 
containing  some  water,  the  residue  is  then 
boiled  with  some  water,  filtered  hot,  and  the 
filtrate  added  to  the  hydrochloric  solution. 

«<*.   The  filtrate  becomes  turbid  and  milky  ; 
this  indicates  ANTIMONY  OR  BISMUTH  ;  or  it 
deposits  fine  crystals  ;  this  indicates  the  pre- 
sence of  LEAD.     The  filtrate  is  heated  again 
8* 


190  '     DIVISION    OF    METALS. 

(if  needed,  wilh  the  addition  of  some  hydro- 
chloric acid)  till  it  appears  clear,  and  then 
treated,  according  to  §  114.  II. 

,fl/3.  The  Jiltrate  remains  clear.  A  few 
drops  of  it  are  evaporated  to  satisfy  ourselves 
whether  the  hydrochloric  acid  has  dissolved 
anything.  If  any  residue  remains,  the  filtrate 
is  treated  according  to  §  114,  II. 
3.  If  boiling  concentrated-  hydrochloric  acid  has  left  a 

residue,  it  is  washed  with  water,  and  treated  as  directed, 

§  127. 

B.  THE  SUBSTANCE  UNDER  EXAMINATION  IS  A  METAL  OR 
AN  ALLOY. 

The  metals  are  best  divided  according  to  their  beha- 
viour with  nitric  acid. 

I.  METALS  WHICH  ARE  NOT  AFFECTED  BY  NITRIC  ACID  : 
gold,  platinum. 

II.  METALS    WHICH    ARE   OXIDIZED   BY    NITRIC    ACID, 

BUT     THE     OXIDES    OF     WHICH    DO     NOT     DISSOLVE    IN     AN 

EXCESS  OF  THE  ACID:  antimony  tin. 

III.  METALS    WHICH  ARE  OXIDIZED  BY   NITRIC    ACID, 

iAND    THE    OXIDES    OF    WHICH    DISSOLVE    IN    AN    EXCESS    OF 

THE  ACID,  FORMING  NITRATES:  all  other  metals. 

A  specimen  of  the  substance  is  drenched  with  nitric 
acid  of  1*25  sp.  gr.,  and  heated. 

1.  COMPLETE  SOLUTION  TAKES  PLACE,  OR  is  EFFECT- 
ED BY  THE  ADDITION  OF  WATER;  this  indicates  the 
absence  of  platinum,  gold,  antimony,  and  tin ;  a  small  spe- 
cimen of  the  solution  is  diluted  with  much  water. 

a.  The  solution  remains  clear ;  some  hydrochloric  acid 
is  added ;  if  this  produces  a  white  precipitate,  which 
does  not  dissolve?  on  heating  the  fluid,  but  is  dissolved 
by  ammonia,  after  having  been  rinsed  previously, 
SILVER  is  present.  The  original  solution  is  treated 
as  directed  §  115. 

b.  The  solution  becomes  turbid  and  milky ;  this 
indicates  the  presence  of  BISMUTH.     The  solution  is 


SOLUTION.  191 

filtered,  and  the  filtrate  tested  for  silver,  as  stated,  § 
106,  B,  1,  a.  The  original  solution  is  treated  accord- 
ing to  §  115. 

2.    A    RESIDUE   REMAINS. 

a.  A  metallic  residue  remains.  The  solution  is 
filtered,  and  the  filtrate  treated  as  directed  §  106,  B,  1 , 
after  having  examined  whether  anything  has  been  dis- 
solved. The  residue  is  by  rinsing  freed  from  all  dis- 
solved metallic  particles,  dissolved  in  aqua  regia,  and 
divided  into  two  portions ;  chloride  of  potassium  is 
added  to  one  portion :  if  a  yellow  precipitate  is  formed, 
it  indicates  the  presence  of  PLATINUM.  Protosulphate 
of  iron  is  added  to  the  other  portion  :  if  a  black  pre- 
cipitate is  formed,  it  indicates  the  presence  of  GOLD. 

6.  A  white  pulverulent  residue  remains  ;  this  indi- 
cates the  presence  of  ANTIMONY  OR  TIN.  The  solution 
is  filtered,  and  the  filtrate  treated  as  directed  §  106, 
B,  1,  after  having  examined  whether  ^jything  has 
been  dissolved.  The  residue  is  carefully  rinsed,  and 
heated  with  a  hot  saturated  solution  of  bitartrate  of 
potash  or  a  solution  of  tartaric  acid. 

<*.  Complete  solution  takes  place  :  this  indicates 
the  presence  of  oxide  of  ANTIMONY  alone;  the 
solution  is  tested  with  solution  of  sulphuretted 
hydrogen, 

/3.  A  white  precipitate  remains,  even  after  boiling 
with  a  fresh  portion  of  solution  of  bitartrate  of  potash 
or  of  tartaric  acid",  this  indicates  the  probable  pres- 
ence of  tin.  The  solution  is  filtered  and  mixed  with 
solution  of  sulphuretted  hydrogen.  If  an  orange-red 
precipitate  is  formed,  oxide  of  antimony  is  present. 
The  presence  of  oxide  of  tin  is  ascertained  by  mixing 
the  residue  with  cyanide  of  potassium  and  carbonate 
of  soda,  and  reducing  it  before  the  blow-pipe. 
(Compare  §  94,  c,  7.) 


192  SUBSTANCES    SOLUBLE    IN    WATER. 

III.     REAL  EXAMINATION. 

Compounds  supposed  to  consist  simply  of  one  base  and  one 
acid  ;  or  one  metal  and  one  metalloid. 

A.     SUBSTANCES  SOLUBLE  IN  WATER. 

Detection  of  the  base.* 

§  107. 

1.  Some  Hydrochloric  acid  is  added  to  a  portion  of  the 
aqueous  solution. 

a.  No  PRECIPITATE  is  FORMED;  this  indicates  the 
absence  of  silver  and  protoxide  of  mercury  with  cer- 
tainty, and  is  also  a  probable  indication  of  the  absence 
of  lead.     For  further  examination,  vide  §  107,  2. 

b.  A  PRECIPITATE  is  FORMED.      Divide  the  fluid, 
in  which  the  precipitate  is  suspended,  into  two  por- 
tions, and  add  ammonia  in  excess  to  the  one. 

ef  The  precipitate  vanishes,  and  the  fluid  be- 
comes clear ;  the  precipitate  in  this  case  consists 
of  chloride  of  silver,  and  is,  therefore,  indicative  of 
the  presence  of  SILVER.  To  obtain  a  conviction 
on  this  point  the  original  solution  must  be  tested 
,  with  chromate  of  potash,  and  with  sulphuretted 

hydrogen.     (Vide  §  90,  0,  2,  and  96,  b,  5-) 
K:.f^/3.   The  precipitate  becomes  black;    it  consists 
'•-ul. -this  case   of   protochloride  of   mercury,  whicb 
has  been  converted  by  the  ammonia  into  protoxide 
of  mercury,  and  is,  consequently,  indicative  of  the 
presence  of  PROTOXIDE  OF  MERCURY.     To  set  all 
doubt  at  rest  as  to  this  point,  test  the  original  solu- 
tion with   protochloride  of  tin  and  with  metallic 
copper.     (Vide  §  90,  5.) 

y.  The  precipitate  remains  unaltered  /  it  con- 
sists in  this  case  of  chloride  of  lead,  which  is  nei- 
4her  decomposed  nor  dissolved  by  ammonia  ;  this 
reaction  is,  therefore,  indicative  of  the  presence  of 
LEAD.  We  assure  ourselves  of  the  presence  of 
this  substance  ;  1st,  by  diluting  the  second  portion 
of  the  fluid  in  which  the  precipitate  produced  by 

*We  include  here  arsenious  and  arsenic  acid. 


SUBSTANCES    SOLUBLE   IN   WATER.  193 

hydrochloric  is  suspended,  with  much  water  and 
applying  heat.     The  precipitate  must  dissolve  if  it 
really  is  chloride  of  lead  ;  2d,  by  adding  dilute  sul- 
phuric acid  to  the  original  solution,  (§  90,  c.) 
2.  Solution  of  sulphuretted  hydrogen  is  added  to  the 
fluid  acidified  with  hydrochloric  acid,  till  it  has  imparted 
its  characteristic  odour  to  this  fluid,  which  the  latter  must 
still  retain  even  after  stirring  and  shaking ;  the  liquid  is 
then  heated. 

a.  THE  FLUID  REMAINS  CLEAR.     Pass  over  to  3, 
for  lead,  bismuth,  copper,  cadmium,  peroxide  of  mer- 
cury, gold,  platinum,  tin,  antimony,  arsenic,  and  pe- 
roxide of  iron,  are  not  present. 

b.  A.    PRECIPITATE    IS    FORMED. 

a.  THIS  PRECIPITATE  is  WHITE  ;  it  is  in  this 
case  produced  by  the  separation  of  sulphur,  and  is 
indicative  of  the  presence  of  PEROXIDE  OF  IRON. 
(§  88,  /.)  The  original  solution  is  then  further 
tested  with  ammonia  and  with  ferrocyanide  of  po- 
tassium, in  order  to  ascertain  whether  the  sub- 
stance present  is  really  peroxide  of  iron. 

p.  THE  PRECIPITATE  is  YELLOW;  in  this  case 
it  may  consist  either  of  sulphuret  of  cadmium,  or 
a  sulphuret  of  arsenic,  or  bisulphuret  of  tin,  and  in- 
dicates therefore  the  presence  either  of  cadmium, 
or  of  arsenic,  or  of  peroxide  of  tin.  To  distinguish 
them,  ammonia  in  excess  is  added  to  the  fluid, 
wherein  the  precipitate  is  suspended. 

aa.  The  precipitate  does  not  disappear  ;  CAD- 
MIUM is  present,  sulphuret  of  cadmium  being  so- 
luble in  ammonia.  The  blow-pipe  is  resorted 
to  for  further  proof.  (§91,  d.) 

bb.  The  precipitate  disappears.  It  consists 
either  of  peroxide  of  tin  or  of  arsenic.  Ammo- 
nia is  added  to  a  portion  of  the  original  solu- 
tion. 

a*.  A  white  precipitate  is  formed-  PE- 
ROXIDE OF  TIN  is  the  substance  present.  As 
a  conclusive  proof,  the  precipitate  is  then 
mixed  with  cyanide  of  potassium  and  carbo- 
nate of  soda,  and  reduced  before  the  blow- 
pipe. (§  94,  6.) 


1  94  DETECTION    OF    THE    BASES. 

AS.  No  precipitate  is  formed.  This  indi" 
cates  the  presence  of  ARSENIC.  The  real 
presence  of  the  arsenic  may  then  be  ascer- 
tained by  the  production  of  a  metallic  crust, 
either  from  the  original  substance,  or  from  the 
precipitated  sulphuret  of  arsenic,  mixed  with 
cyanide  of  potassium  and  carbonate  of  soda, 
or  in  some  other  way,  and  also  by  mixing  the 
original  substance  with  carbonate  of  soda,  and 
exposing  it  to  the  reducing  flame  of  the  blow- 
pipe. (§  94,  d.) 

V.    THE    PRECIPITATE  IS    ORANGE  COLOURED  J  in 

this  case  it  consists  of  sulphuret  of  antimony,  and 
indicates  the  presence  of  OXIDE  OF  ANTIMONY.  The 
blow-pipe  is  resorted  to  for  further  proof.  (§  94,  a.) 

&.    THE   PRECIPITATE  IS    BROWN.       It  Consists   of 

sulphuret  of  tin,  and  indicates  the  presence  of 
PROTOXIDE  OF  TIN.  For  conclusive  proof,  one 
portion  of  the  original  solution  is  tested  with  so- 
lution of  perchloride  of  mercury,  and  another  with 
solution  of  gold.  (§  94,  b.) 

e.  THE  PRECIPITATE  is  BLACK.  It  may  in  this 
case  consist  of  sulphuret  of  lead)  or  sulphuret  of 
copper,  or  sulphuret  of  bismuth,  or  sulphuret  of  gold, 
or  sulphuret  of  platinum,  or  bisulphuret  of  mercury. 
To  distinguish  these  from  each  other,  the  following 
experiments  are  made  with  the  original  solution. 

aa.  Dilute  sulphuric  acid  is  added  to  a  portion 
of  it ;  a  white  precipitate  is  formed  ;  this  indicates 
the  presence  of  LEAD.  Chromate  of  potash  is  em- 
ployed as  a  conclusive  test.  (§  90,  c.) 

bb.  Ammonia  in  excess  is  added  to  a  portion  of 
it.  A  blue  precipitate  is  formed  which  redissolves 
in  the  excess  of  the  precipitant,  imparting  an  azure 
colour  to  the  solution  ;  this  indicates  COPPER.  Fer- 
rocyanide  of  potassium  is  resorted  to  as  a  conclu- 
sive test.  (§91,  b.) 

cc.  Potash  is  added  to  a  portion  of  it.  A  yellow 
precipitate  is  formed ;  this  indicates  the  presence 
of  PEROXIDE  OF  MERCURY.  Protochloride  of  tin 
and  metallic  copper  are  employed  as  conclusive 


SUBSTANCES  SOLUBLE  IN  WATER.  195 

tests.  (§91,  a.)  The  presence  of  peroxide  of  mer- 
cury may  generally  also 'be  detected  by  the  preci- 
pitate which  it  yields  with  sulphuretted  hydrogen, 
not  appearing  black  from  the  beginning,  but  on  the 
addition  of  an  excess  of  the  precipitant,  passing 
through  white,  yellow,  and  orange,  and  then  at  last 
changing  its  colour  into  black.  (§91,  «,  2.) 

dd.  A  portion  of  the  original  solution  is  evapo- 
rated nearly  to  dryness,  in  a  porcelain  crucible,  and 
the  residue  put  into  a  test  tube,  half  filled  with 
water.  If  the  solution  becomes  milky,  a  basic 
salt  of  bismuth  is  present ;  this  reaction,  therefore, 
indicates  BISMUTH.  The  blow-pipe  is  resorted  to, 
as  a  conclusive  test.  (§91,  c.) 

ee.  Solution  of  sulphate  of  iron  is  added  to  a 
portion  of  the  original  solution.  A  fine  black  pre- 
cipitate is  indicative  of  the  presence  of  GOLD.  The 
blow-pipe  is  resorted  to  as  a  conclusive  test ;  or 
the  original  solution  is  tested  with  protochloride  of 
tin.- (§93,  a.) 

ff.  Chloride  of  potassium  is  added  to  a  portion 
of  the  original  solution ;  the  formation  of  a  yellow 
crystalline  precipitate  is  indicative  of  the  presence 
of  PLATINUM.  For  further  proof  this  precipitate  is 
heated  to  redness.  (§  93,  6.) 

3.  To  the  fluid  in  which  sulphuretted  hydrogen  has  not 
produced  any  precipitate,  or — should  this  have  become  too 
dilute — to  a  portion  of  the  original  solution,  ammonia  is 
added,  till  the  solution  has  an  alkaline  reaction  ;  hydrosul- 
phuret  of  ammonia  is  then  added.  (If  the  solution  was 
not  acid,  and  thus  no  ammoniacal  salt  has  been  formed  on 
the  addition  of  ammonia,  the  addition  of  the  hydrosulphu- 
ret  of  ammonia  is  preceded  by  that  of  sal  ammoniac.) 

a.  No   PRECIPITATE   is   FORMED  ;    pass    over   to 
§  107,  4  ;  for  iron,  cobalt,  nickel,  manganese,   zinc, 
chromium,  and  alumina  are  not  present. 

b.  A  PRECIPITATE  IS  FORMED. 

*.  The  precipitate  is  black  ;  protoxide  of  iron, 
nickel,  or  cobalt.  A  portion  of  the  original  solution 
is  treated  with  caustic  potash. 

aa.  A  dirty  greenish  white  precipitate  is  ob- 


196  DETECTION  OF  THE  BASES. 

tained,  which  soon  changes  into  a  reddish-brown, 
when  exposed  to  the  air  :  PROTOXIDE  OF  IRON. 
Ferricyanide  of  potassium  is  resorted  to  as  a 
conclusive  test.  (§  88,  e.) 

bb.  A  precipitate  of  a  light  greenish  tint  is 
producedj  which  does  not  change  its  colour  : 
NICKEL.  Ammonia  and  addition  of  potash  are 
resorted  to  as  conclusive  tests.  (§  88,  c.) 

cc.  A  sky-blue  precipitate  is  formed,  which 
changes  its  tint  into  red,  on  boiling  :  COBALT. 
The  blow-pipe  is  resorted  to  as  a  conclusive  test. 
§  88,  d.) 
/s.  The  precipitate  is  not  black. 

aa.  If  the  precipitate  is  of  a  clear  flesh  colour, 
it  consists   of  sulphuret  of  manganese,  and  is, 
therefore,  indicative  of  the  presence  of  PROTOX- 
IDE OF  MANGANESE.     The  addition  of  potash  to 
the    original    solution,    or    the    blow-pipe,   are 
resorted  to  as  conclusive  tests.  (§  88,  b.) 
bb.  If  the  precipitate  is  bluish-green,  it  consists  of 
hydrated  OXIDE  OF  CHROMIUM.     The  addition  of  pot- 
ash to  the  original  solution,  and  the  blow-pipe  are  re- 
sorted to  as  conclusive  tests.     (§  87,  b.) 

cc.  If  the  precipitate  is  white,  it  may  consist  eith- 
er of  hydrate  of  alumina,  or  of  sulphuret  of  zinc,  and 
thus  be  indicative  of  the  presence  either  of  alumina  or 
of  oxide  of  zinc.  To  distinguish  these,  solution  of 
potash  is  gradually  dropped  into  a  portion  of  the  ori- 
ginal solution,  till  the  precipitate  is  redissolved,  and 
then 

*&.  Solution  of  sulphuretted  hydrogen  is  added  to 
a  portion  of  it  ;  the  formation  of  a  white  precipi- 
tate is  indicative  of  the  presence  of  zinc.  For  fur- 
ther proof,  the  reaction  with  solution  of  cobalt  be- 
fore the  blow-pipe  is  selected.  (§  88.  a.) 

/3j8.  Muriate  of  ammonia  is  added  to  another  por- 
tion of  the  alkaline  solution.  The  formation  of  a 
white  precipitate  is  indicative  of  the  presence  of  AL- 
UMINA. The  test  with  solution  of  cobalt  before 
the  blow-pipe  is  selected  as'  a  conclusive  proof.  (§ 
87.  a.) 


SUBSTANCES    SOLUBLE   IN    WATER.  197 

Note  to  §  107.  3.  /3. 

As  very  slight  contaminations  may  impair  the  distinct- 
ness of  the  tints  which  the  precipitates  considered  under  § 
107.  3.  6. /3  present,  it  is  advisable  where  such  are  sus- 
pected to  adopt  the  following  method  for  the  detection  of 
manganese,  chromium,  zinc,  and  alumina. 

Potash  in  excess  is  added  to  a  portion  of  the  original 
solution. 

aa.  A  whitish  precipitate  is  formed,  which  is  not 
redissolved  in  an  excess  of  the  precipitant,  and  soon 
changes  its  colour  to  a  blackish  brown  when  exposed 
to  the  air  :  MANGANESE.  The  blow-pipe  is  resorted 
to  as  a  conclusive  test.  (§  88,  6.) 

bb.  A  precipitate  is  formed  which  redissolves  in 
an  excess  of  the  precipitant :  oxide  of  chromium,  alu- 
mina, zinc. 

««<*.  Sulphuretted  hydrogen  is  added  to  a  portion 
of  the  solution  with  potass.  The  formation  of  a 
white  precipitate  indicates  the  presence  of  ZINC. 

/3/3.  If  the  original  or  solution  with  potass  appear 
green,  and  the  precipitate,  first  produced  by  potash 
and  then  redissolved  in  the  excess  of  the  precipi- 
tant, was  bluish,  OXIDE  OF  CHROMIUM  is  present. 
For  further  proof,  the  solution  with  potass  may  be 
boiled,  or  the  blow-pipe  resorted  to.  (§  87,  b.) 

yy.  Muriate  of  ammonia  is  added  to  the  solution 
with  potass.  The  formation  of  a  white  precipitate 
indicates  the  presence  of  ALUMINA.  The  test  with 
solution  of  cobalt  before  the  blow-pipe  is  selected 
as  a  further  proof,  (§  87,  a.} 

4.  Muriate  of  ammonia  and  carbonate  of  ammonia,  mix- 
ed with  a  small  quantity  of  caustic  ammonia,  are  added  to 
a  portion  of  the  original  solution,  which  is  then  BOILED. 

a.  No  PRECIPITATE  is  FORMED  :  absence  of  bary- 
tes,  strontian,  or  lime.     Pass  over  to  §  107, 5. 

b.  A  PRECIPITATE  is  FORMED      Presence  of  bary- 
tes,  strontian,  or  lime.     Solution  of  gypsum  is  added 
to  a  portion  of  the  original  solution,  and  heat  applied. 

«.  The  solution  does  not  become  turbid  even  af- 
ter the  lapse  of  Jive  to  ten  minutes  :  LIME.  The 


198  DETECTION    OF    THE    BASES. 

test  with  oxalic  acid  is  selected  for  further  proof. 
(§86,c.) 

/3.  The  solution  does  not  become  turbid  at  first, 
but  after  the  lapse  of  some  time  :  STRONTIAN.  The 
alcohol  flame  is  resorted  to  as  a  conclusive  test. 
(§  86,^.). 

y.  A  precipitate  is  immediately  formed :  BARY- 
TES.  For  further  proof,  test  with  hydrofluosilicic 
acid.  (§  86,  a.) 

5.  Phosphate  of  soda  is  added  to  the  solution  of  (4)  in 
which  carbonate  of  ammonia,  after  the  addition  of  muriate 
of  ammonia  has  produced  no  precipitate. 

a.  No  PRECIPITATE  is  FORMED,  not  even  after  agi- 
tating the  solution  :  absence  of  magnesia.     Pass  over 
to  §  107,  6. 

b.  A  FINE    CRYSTALLINE  PRECIPITATE   IS  FORMED  I 
MAGNESIA. 

6.  A  drop  of  the  original  solution  is  evaporated   on  a 
platinum  plate  and  the  residue  heated  to  redness. 

a.  No  FIXED  RESIDUE  REMAINS.     The  original  so- 
lution is  tested  for  AMMONIA,  by  adding  potash  to  it, 
and  examining  the  odour,  the  vapours  formed  with 
acetic  acid,   and  the  reaction  of   the  escaping  gas. 
($  85,  c.) 

b.  A    FIXED    RESIDUE    REMAINS.       Potash    OF    Soda. 

Tartaric  acid  is  added  to  a  portion  of  the  original 

solution,  and  the  latter  well  shaken. 

<*.  'No  precipitate  is  formed,  not  even  after  the 
lapse  of  ten  to  fifteen  minutes  :  SODA.  The  blow- 
pipe flame  and  alcohol  flame,  and  especially  the 
reaction  with >  antimoniate  of  potash,  are  selected 
as  conclusive  tests.  (§  85,  b.) 

, . .  ]  /3.  A  crystalline  granular  precipitate  is  formed : 
POTASH.  Chloride  of  platinum,  1  the 'blow-pipe 
flame,  "and  alcohol  flame,  are  selected  as  conclusive 
tests.  (§  85,  a.). 

Compounds  which  are  supposed  to  contain  but  one 
acid  and  one  base,  fyc. 


DETECTION    OF    INORGANIC   ACIDS.  199 

A.    SUBSTANCES  SOLUBLE  IN   WATER.       DETECTION  OF  THE 
ACID. 

I.     Detection  of  inorganic  acids. 
$  108. 

We  must  in  the  first  place  consider  what  acids  form 
combinations  soluble  in  water,  with  the  base  detected,  and 
bear  it  in  mind  in  the  subsequent  examination. 

1.  We  have  already  spoken  of  the   detection  of  the 
ARSENIOUS  and  ARSENIC  ACID  in  treating  of  the  detection 
of  the  bases.     They  are  distinguished  from  each  other  by 
their  behaviour  with  nitrate  of  silver,  or  with  potash  and 
sulphate  of  copper.     (§  94,  d  and  e.) 

2.  The  detection  of  CARBONIC  ACID,   HYDROSULPHURIC 
ACID  and  CHROMIC  ACID,  has  also  already  been  pointed  out, 
when  treating  of  the  detection  of  the   bases.     The  two 
former  betray  their  presence  by  effervescing  on  the  addi- 
tion of  hydrochloric  acid ;  they  may  be  distinguished  from 
each  other  by  their  odour,  and  if  needed,  the  presence  of 
carbonic  acid  may  be  proved  by  its  reaction  with  lime- 
water,  (§  99,  a,)  and  that  of  sulphuretted  hydrogen  by  the 
reaction  with  solution  of  lead.  (§  100,  e.)     Chromic  acid 
may,  in  most  cases,  be  detected  by  the  yellow  or  red  tint 
of  its   solution,  and  also  by  its   solution   changing  colour 
and  yielding  a  precipitate  of  sulphur,  on  the   addition  of 
sulphuretted  hydrogen.     We  may  assure  ourselves  of  the 
presence  of  chromic  acid  by  the  reaction  with  solution  of 
lead,  and  solution  of  silver.     (§  96,  b.) 

3.  Chloride  of  barium  is.  added  to  a  portion  of  the  solu- 
tion ;  should  the  latter  have  an  acid  reaction,  it  must  first 
be  neutralized  or  rendered  feebly  alkaline,  by  the  addition 
of  ammonia. 

a.  THE  FLUID  REMAINS  CLEAR.  (Pass  over  to 
§  1Q8,  4.)  The  absence  of  sulphuric  acid,  phospho- 
ric acid,  and  silicic  acid  is  certain,  that  of  oxalic  acid 
and  boracic  acid,  probable.  For  the  barytes  com- 
pounds of  these  two  latter  acids  are  kept  in  solution 
by  ammoniacal  salts,  and  borate  of  barytes  does  not 
at  all  precipitate  from  dilute  solutions. 


200  DETECTION    OP    INORGANIC    ACIDS. 

b.  A  PRECIPITATE  is  FORMED.  Hydrochloric  acid 
is  added  in  excess. 

<*.  The  precipitate  redissolves.  Absence  of  sul- 
phuric acid.  Pass  over  to  4. 

/3.  The  precipitate  remains  and  does  not  dissolve 
even  in  a  large  proportion  of  water :  SULPHURIC 
ACID. 

4.  Solution  of  gypsum  is  added  to  a  portion  of  the  ori- 
ginal solution,   which,  should  it   have   an  acid  reaction, 
must  first  be  rendered  neutral  or  feebly  alkaline,    by  the 
addition  of  ammonia. 

a.  No  PRECIPITATE  is  FORMED  i  absence  of  oxalic 
acid  and  phosphoric  acid.  Pass  over  to  §  108,  5. 

6.  A  PRECIPITATE  is  FORMED.  Acetic  acid  is 
added  in  excess. 

*.  The  precipitate  is  redissolved  :  PHOSPHORIC 
ACID.  The  reactions  with  sulphate  of  magnesia 
and  ammonia,  with  solution  of  silver,  and  before 
the  blow-pipe,  are  selected  as  conclusive  tests. 
(§  98,  a.} 

p.  .The  precipitate  remains  undissolved,  but 
dissolves  readily  in  hydrochloric  acid :  OXALIC  ACID. 
The  reaction  with  concentrated  sulphuric  acid  is 
selected  as  a  conclusive  test.  (§  98,  c.) 

5.  A  fresh  portion  of  the  original  solution  is   acidified 
with  nitric  acid,  and  solution  of  nitrate  of  silver  is  then 
added. 

a.  THE  FLUID  REMAINS  CLEAR.     This  is  a  certain 
indication  of  the  absence  of  chlorine  and  iodine.  The 
absence  of  cyanogen  is  also  probable.     For  cyanide 
of  mercury  is  not  precipitated   by   nitrate  of  silver ; 
and  from  the  detected  base  we  may  conclude  whether 
we  have  to  look  for  the  presence  of  this  substance  or 
not ;   for  the  manner  in  which   the  presence  of  the 
cyanogen  in  it  is  proved,  we  refer  to  §  100,  d.     Pass 
over  to  §  108,  6. 

b.  A  PRECIPITATE  is  FORMED.  Ammonia  is  added 
in  excess. 

«.  The  precipitate  does  not  dissolve  IODINE. 
As  a  conclusive  test,  we  select  the  reaction  with 
starch.  (§  100,  c.) 


DETECTION  OF  ORGANIC  ACIDS.          201 

/3.  The  precipitate  is  redissolved.  If  it  redis- 
solves  readily,  we  have  reason  to  suppose 
that  CHLORINE  is  present;  if  it  dissolves  with 
difficulty  and  only  on  the  addition  of  much  ammo- 
nia, we  may  suppose  that  CYANOGEN  is  present. 
We  assure  ourselves  of  the  presence  of  chlorine, 
by  testing  the  original  solution  with  protonitrate  of 
mercury,  and  by  the  behaviour  of  the  silver  preci- 
pitate formed  when  exposed  to  a  high  temperature. 
(§  100,  a.)  The  presence  of  cyanogen  may  be 
further  proved  by  adding  potash,  solution  of  mag- 
netic oxide  of  iron  and  hydrochloric  acid  to  the 
original  solution.  (§  100,  d.) 

6.  A  portion  of  the  solid  substance — (or  if  we  have  a 
fluid  to  operate  upon,  the  residue  obtained  by  evaporation) 
— is  drenched  with  some  sulphuric  acid,  alcohol  added,  and 
then  kindled.     BORACIC  ACID  is  present  if  the  flame  ap- 
pears green  on  stirring. 

7.  The   preliminary   examination  generally  enables  us 
to  detect  nitric  acid.  ($  105,  A,  I,  2,  c.)  The  reactions  with 
sulphate  of  iron  and  sulphuric  acid,  or  solution  of  indigo, 
are  selected  as  conclusive  proofs.     (§  101,  a.) 

8.  We  refer  to  §  123  for  the  detection  of  chloric  acid, 
hydrofluoric  acid,  cilicic  acid,  and  bromine. 

Compounds  which  we  suppose  to  contain  only  one  acid 
and  one  base,  $*c. 

A.   SUBSTANCES  SOLUBLE  IN  WATER.    DETECTION  OP 

THE    ACID. 

II.    DETECTION    OF     ORGANIC    ACIDS. 
§    109. 

1.  To  a  portion  of  the  aqueous  solution,  ammonia  is 
added  till  a  feeble  alkaline  reaction  becomes  manifest,  and 
then  chloride  of  calcium.  If  we  have  to  operate  upon  a 
neutral  solution,  some  muriate  of  ammonia  is  added  to  it, 
previous  to  the  addition  of  the  chloride  of  calcium. 

a.  No  PRECIPITATE  IS  FORMED,  NOT  EVEN  AFTER  JLGI- 


202  DETECTION   OF    ORGANIC    ACIDS. 

TATING  THE    SOLUTION,  NOR  AFTER;  THE  LAPSE    OF  A  FEW 

MINUTES  :  absence  of  oxalic  acid  and  tartaric  acid. 

Pass  over  to  §  1 09,  2. 

b.  A    PRECIPITATE    is    FORMED.     Lime-water  is 

added  in  excess  to  a  portion  of  the  original  solution, 

and  the  precipitate  formed  treated  with   solution   of 

sal  ammoniac. 

et.  The  precipitate  vanishes:  TARTARIC  ACID. 
The  reaction,  with  acetate  of  potash  may  be  re- 
sorted to  for  further  proof;'  but  the  safest  test  is 
the  behaviour  of  the  precipitate  produced  by  chlo- 
ride of  calcium,  with  caustic  potash.  (§  102,  6.) 
/3.  The  precipitate  does  not  vanish :  OXALIC 

ACID. 

2.  The  fluid  of   1,  a,  is  heated  to  boiling,  kept  at  the 
boiling   point  for   some  time,  and  some  ammonia  added 

whilst  boiling.) 

a.'  IT  REMAINS  TRANSPARENT;  no  citric  acid.  Pass 
over  to  §  109,  3. 

6.    IT   BECOMES  TURBID,     AND    DEPOSITS   A   PRECIPI- 
TATE I    CITRIC  ACID. 

3.  The  fluid  of  2,  a,  is  mixed  with  alcohol. 

a.  IT    REMAINS   TRANSPARENT  i    no  malic    acid. 
Pass  over  to  §  109,  4. 

b.  A   PRECIPITATE  IS    FORMED:    MALIC  ACID.       The 

re-action  with  acetate  of  lead  is  selected  as  a  conclu- 
sive test.     (§  102,  e.) 

4.  A  portion  of  the  original  solution  is  rendered  perfectly 
neutral — (if  it  is  not  already  so) — by  ammonia  or  hydro- 
chloric acid,  and  solution  of  perchloride  of  iron  added. 

a.  A  CINNAMON-COLOURED  OR  DIRTY  YELLOW  BUL- 
KY  PRECIPITATE    is    FORMED..   This   precipitate  is 
treated  with  dilute  hydrochloric  acid. 

«.  It  dissolves  transparent ;  SUCCINIC  ACID. 

/3.  It  dissolves,  with  the  separation  of  a  white 
precipitate:  BENZOIC  ACID.  We  assure  ourselves 
of  the  real  presence  of  this  substance,  by  heating 
the  precipitate.  It  must  manifest  the  properties  of 
free  benzoic  acid.  (Vide  §  103,  b.) 

b.  THE     LIQUID    ASSUMES    AN    INTENSE    RED    TINT, 
AND   UPON   BOILING    FOR     SOME    TIME,    A    LIGHT     RED- 
DISH-BROWN PRECIPITATE  SEPARATES:   acetic  acid  or 


SUBSTANCES    INSOLUBLE    IN    WATER.  203 

formic  acid.  A  portion  of  the  solid  salt  under  exami- 
nation, or  the  residue  obtained  by  evaporating  the 
liquid — (if  the  liquid  is  acid,  it  must  be  neutralized 
with  potash,  previous  to  the  evaporation) — is  heated 
with  sulphuric  acid  and  alcohol,  (§  104,  a.)  The  cha- 
racteristic odour  of  acetic  ether,  indicates  the  presence 

of  ACETIC   ACID. 

If  we  do  not  detect  acetic  acid  in  the  fluid,  we 
must  conclude  that  the  substance  under  examination 
contains  FORMIC  ACID:  the  certain  presence  of  this 
latter  substance  may  be  proved  by  its  behaviour  with 
nitrate  of  silver  and  protoxide  of  mercury.  (§  104,  6.) 

Compounds  which  are  supposed  to  consist  of  but  one  acid 
and  one  base. 

B.     SUBSTANCES    INSOLUBLE    OR    SPARINGLY    SOLUBLE    IN 

WATER,     BUT     SOLUBLE     IN    HYDROCHLORIC     ACID,     NITRIC 
ACID,    OR    AQUA    REG1A. 

Detection  of  the  base.* 
§  110. 

A  portion  of  the  solution  in  hydrochloric  acid,  nitric  acid, 
or  aqua  regia,  is  diluted  with  water,!  and  the  further 
operations  conducted  exactly  as  directed  §  107,  beginning 
at  1,  when  the  substance  is  dissolved  in  nitric  acid,  and  at 
2,  when  it  contains  already  hydrochloric  acid.  The  follow- 
ing circumstances  must  be  well  attended  to '.  we  have  seen 
that  if  in  cases  where  we  have  A  SUBSTANCE  SOLUBLE  IN 
WATER  before  us,  we  obtain  in  the  course  of  the  examina- 
tion, a  white  precipitate  on  testing  with  hydrosulphuret  of 
ammonia — (after  having  neutralized  with  ammonia  the  free 
acid  either  originally  contained  in  or  previously  added  to 
the  solution  under  examination)  this  precipitate  can  consist 
only  either  of  sulphuret  of  zinc,  or  of  alumina.  But  the 
case  is  different,  when  the  substance  is  INSOLUBLE  IN 

*  Regard  has  here  been  had  also  to  several  salts,  since  this  course 
of  examination  directly  leads  to  their  detection. 

flf,  on  the  addition  of  the  water,  the  liquid  becomes  turbid  or  is 
precipitated,  it  indicates  the  presence  of  antimony,  bismuth,  or  tin. 
(Compare  $  105,  B  4.) 


204  SUBSTANCES    SOLUBLE    IN    WATER. 

'_» 

WATER,  but  dissolved  by  hydrochloric  acid ;  for  in  that  case 
the  white  precipitate  produced  by  hydrosulphuret  of  ammo- 
nia, with  the  presence  of  sal  ammoniac,  may  also  consist 
of  a  phosphate  of  the  alkaline  earths  as  well  as  of  oxalate  of 
lime,  (barytes  and  strontian.)  If,  therefore,  we  obtain  a 
white  precipitate  when  testing  an  acid  solution,  under  the 
circumstances  stated,  and  as  directed  §  107,  at  3  /3.  cc,  the 
following  method  must  be  employed.  Caustic  potash  in 
excess  is  added  to  a  small  portion  of  the  original  hydrochlo- 
ric solution. 

1.    THE  PRECIPITATE  AT  FIRST  FORMED,  REDISSOLVES  IN 

EXCESS  OF  THE  PRECIPITANT  }  absence  of  the  salts  of  the  al- 
kaline earths  ;  presence  of  zinc  or  of  alumina  :  to  distinguish 
these  from  each  other,  the  solution  with  potass  is  tested 
with  sulphuretted  hydrogen  and  muriate  of  ammonia.  (Vide 
supra  §  107,  3  b.  /3  cc.)  Alumina  may  have- been  present 
and  precipitated  as  phosphate  of  alumina.  This  is  ascer- 
tained by  dissolving  the  precipitate  in  hydrochloric  acid, 
adding  tartaric  acid,  supersaturating  with  ammonia  and 
mixing  with  sulphate  of  magnesia.  If  phosphoric  acid  is 
present,  a  precipitate  of  basic  phosphate  of  ammonia  and 
magnesia  is  formed. 

2.    THE  PRECIPITATE    FORMED  DOES    NOT  REDISSOLVE  IN 

AN  EXCESS  OF  THE  PRECIPITANT.  Presence  of  a  phosphate 
or  oxalate  with  an  alkaline  earth  for  its  base.  In  this  case 
a  portion  of  the  original  substance  is  heated  to  redness,  in 
order  to  ascertain  whether  we  have  an  oxalate  or  a  phos- 
phate before  us.  If  the  substance  is  converted  by  this  pro- 
cess into  a  carbonate — (slightly  blackening  or  not  at  all) — 
which  is  easily  detected  by  the  heated  mass  effervescing 
when  treated  with  acids,  whilst  previous  to  the  heating  it 
did  not  present  this  property,  we  may  conclude  that  the 
salt  is  an  OXALATE  ;  if,  on  the  contrary,  no  alteration  takes 
place,  on  the  application  ol  a  red  heat,  we  have  a  PHOS- 
PHATE before  us. 

a.  THIS  PRELIMINARY  EXAMINATION  DENOTED  THE 
PRESENCE  OF  A  PHOSPHATE. 

A  certain,  not  too  inconsiderable  quantity,  of  perchlo- 
ride  of  iron  is  added  to  a  portion  of  the  hydrochloric 
solution,  which  is  then  brought  to  alkaline  reaction  by 
the  addition  of  ammonia,  and  the  liquid  filtered  off 


SUBSTANCES   INSOLUBLE  IN    WATER.  205 

from  the  bulky  precipitate  formed,  which  should  pre- 
sent a  reddish-brown  tint.  In  this  operation  the  phos- 
phoric acid  is  separated  from  its  base,  and,  combined 
with  peroxide  of  iron,  precipitated  together  with  free 
hydrate  peroxide  of  iron,  whilst  the  alkaline  earth  base 
is  contained  in  the  filtered  liquid  as  a  chloride.  The 
further  process  of  the  detection  of  this  base  is  conduct- 
ed as  directed  §  107,  4. 

In  order  to  determine  the  presence  of  the  phospho- 
ric acid  also,  the  iron  precipitate  is  rinsed,  and  di- 
gested with  hydrosulphuret  of  ammonia.  We  obtain 
in  this  process  sulphuret  of  iron  and  phosphate  of  am- 
monia. These  are  separated  from  each  other  by  fil- 
tration, and  sal  ammoniac  and  sulphate  of  magnesia  is 
then  added  to  the  filtered  liquid  ;  the  precipitate 
which  forms,  of  basic  phosphate  of  ammonia  and 
magnesia,  is  a  safe  indication  of  the  presence  of  phos- 
phoric acid.  In  more  minute  examinations,  the  ex- 
cess present  of  hydrosulphuret  of  ammonia  is  first  de- 
composed by  the  addition  of  hydrochloric  acid,  the  so- 
lution heated  to  boiling,  and  the  precipitated  sulphur  fil- 
tered off;  the  filtered  solutions,  if  needed,  concentrated 
by  evaporation,  supersaturated  with  ammonia,  and 
sulphate  of  magnesia  then  added. 

b.  THE  PRELIMINARY  EXAMINATION  INDICATED  THE 
PRESENCE  OF  AN  OXALATE. 

Two  methods  may  be  pursued,  with  certainty,  to 
determine  the  base  and  the  acid. 

1.  A  portion  of  the  compound  is  heated  to  red- 
ness, the  residue  dissolved  in   hydrochloric   acid, 
and  the  alkaline  earth  which  forms  the  base,  de- 
tected in  the  usual  manner  in  this  solution.     Of  the 
presence  of  the  oxalic  acid,  we  assure  ourselves  by 
testing  another  portion  of  the  substance  with  con- 
centrated sulphuric  acid.  (§  98,  c.) 

2.  A  portion  of  the  compound  is  boiled  for  some 
time  in  a  concentrated  solution  of  carbonate  of  pot- 
ash,  and  the  fluid  filtered  from  the  residue.      In 
this  manner  we  obtain  in  the  residue  the  alkaline 
earth  which  forms  the  base  of  the  substance  under 
examination,  combined  with  carbonic  acid,  whilst 

9 


206  DETECTION    OP    INORGANIC    ACIFS. 

we  have  the  oxalic  acid  combined  with  potash  in 
the  filtered  solution;  to  assure  ourselves  of  the 
real  presence  of  this  acid,  the  solution  is  first  acid- 
ified with  acetic  acid,  and  then  treated  with  solution 
of  gypsum.  (§  98,  c.).  The  residue  is  rinsed  and 
dissolved  in  hydrochloric  acid,  and  the  solution 
treated  as  directed  §  107,  4. 

Compounds  which  are  supposed  to  consist  of  but  one  acid 
and  one  base,  fyc. 

B. '  SUBSTANCES     INSOLUBLE    OR   SPARINGLY    SOLUBLE    IN 

WATER,  BUT  SOLUBLE  IN  HYDROCHLORIC  ACID,  NITRIC  ACID* 
OR  AQUA  REGIA. 

DETECTION  OF  THE  ACID. 

1.  Detection  of  inorganic  acids,, 
§  111. 

1.  CHLORIC  ACID  cannot  be  present,  for  all  chlorates  are 
soluble  in  water  ;  the  nitrates  also,  with  the  exception  of  a 
few,  beiag  soluble  in  water,  we  may  generally  disregard 
the  presence  of  NITRIC  ACID.     The  basic  nitrate  of  bismuth 
forms  the  most  frequently  occurring  exception  to  the  gene- 
ral rule  of  solubility  of  the  nitrates  in  water.  The  presence 
of  nitric  acid  in  such  insoluble  compounds  may  be  imme- 
diately detected  by  deflagration  taking  place  when  the 
substance  under  examination  is  thrown  upon  red-hot  char- 
coal.    The  deflagration  which  ensues  on  fusing  a  nitrate 
together  with  cyanide  of  potassium,  is  a  safer  test  of  the 
presence    of  nitric   acid.      (Vide   §    101,   a.)      For   the 
CYANIDES  insoluble  in  water,  we  refer  to  §  1 28. 

2.  The  detection  of  ARSENIOUS  and  ARSENIC  ACID,  CAR- 
BONIC ACID,  HYDROSULPHURIC  ACID,  and  CHROMIC  ACID,  has 

already  been  pointed  out,  when  treating  of  the  detection  of 
bases  ;  as  the  best  tests  and  indications  of  the  presence 
of  chromic  acid,  we  have  pointed  out  the  yellow  or  red 
colour  of  the  compound,  the  evolution  of  chlorine,  upon  a 
chromate  being  boiled  with  hydrochloric  acid,  and  the 
subsequent  detection  of  chromic  oxide  in  the  solution.  But 
the  safest  method,  and  that  which  was  applicable  in  all 


SUBSTANCES    INSOLUBLE    IN  WATER.  207 

cases,  is  to  fuse  the  substance  supposed  to  contain  chromic 
acid,  together  with  some  carbonate  of  soda  and  nitre. 
(§  96,  6.) 

3.  A  portion   of  the   substance  under  examination   is 
boiled  with  nitric  acid. 

a.  If  nitric  oxide  gas  is  evolved,  which  is  easily 
detected  by  the  red  fumes  of  nitrous  acid,  formed  on 
coming  in  contact  with  the  air,  it  indicates  the  pre- 
sence of  a  SULPHURET  }  if  carbonic  acid  is  evolved, 
that  of  a  CARBONATE.     Of  the  presence  of  a  sulphuret 
we  may  easily  assure  ourselves,  by  testing  the  nitric 
solution  with  chloride  of  barium ;  it  should  yield  with 
this  reagent  a  precipitate  of  sulphate  of  barytes,  which 
must  remain  undissolved  even  in  a  large  quantity  of 
water.     Sulphurets  may  as  safely  be  detected  by  their 
behaviour  before  the  blow-pipe.     (Vide  §  100,  c.) 

b.  If  violet  vapours  escape,  the  compound  may  be 
supposed  to  be  an  IODIDE.     A  slip  of  paper,  covered 
with  starch,    forms  the  best  conclusive    test  of  the 
presence  of  iodine.     (§  100,  c.) 

4.  Nitrate  of  silver  is  added  to  a  portion  of  the  nitric 
solution,  (this  solution  must  previously  be  filtered,  if  upon 
treating  the  substance  with  nitric  acid  any  insoluble  residue 
has  remained.)     If  a  white  precipitate  is  formed  soluble  in 
ammonia,  and  fusing  without  decomposition  when  heated, 
it  indicates  the  presence  of  CHLORINE. 

5.  A  portion  of  the  substance  is  boiled  with  hydrochloric 
acid,  filtered,  if  needed,  and  nitrate  of  barytes  added.     The 
formation  of  a  white  precipitate,  which  does  not  disappear, 
even  on  the  addition  of  a  large  proportion  of  water,  indi- 
cates the  presence  of  sulphuric  acid. 

6.  ForBORAcic    ACID,  test  as  stated  supra,  §  108. 

7.  If  none  of  all  these  acids  is  present,  we  have  reason 
to   suppose  the  presence  of  either  PHOSPHORIC  ACID   or 
OXALIC  ACID,  or  the  absence  of  all  acids.     If  the  phosphoric 
acid  had  been  combined  with  an  alkaline  earth,  and  the 
oxalic  acid  with  lime,  (barytes,  or  strontian,)  either  of  them 
would  have  already  been  detected  when  testing  for  these 
bases.  (§110.)    We  may  therefore  disregard  the  presence 
of  these  two  acids,  except  when  other  bases  than  those 
enumerated  are  present.     In  the  latter  case  the  fluid  is 
prepared  for  further  examination  by  precipitating  and  sepa- 


208  DETECTION    OF    ORGANIC    ACIDS. 

rating  the  heavy  metals  from  it — (this  is  effected  in  acid 
solutions  by  means  of  sulphuretted  hydrogen,  and  in  alka- 
line solutions  by  hydrpsulphuret  of  ammonia) — and  is  then 
tested  for  phosphoric  acid  or  oxalic  acid,  as  directed  §  108, 4. 
8.  For  the  detection  of  SILICIC  ACID,  BROMINE,  AND 
FLUORINE,  vide  §  123,  at  the  end. 

Compounds  which  are  supposed  to  consist  of  but  one  base 
and  one  acid,  $*c. 

B.  SUBSTANCES  INSOLUBLE  OR  SPARINGLY  SOLUBLE  IN  WATER, 

BUT    SOLUBLE    IN    HYDROCHLORIC    ACID,    NITRIC    ACID,    OR 
AQUA  REGIA. 

DETECTION   OF  THE  ACID. 

II.  Detection  of  organic  acids.     • 
§  112. 

1.  A  portion  of  the  substance  under  examination  is  dis- 
solved in  the   smallest  possible  quantity  of  hydrochloric 
acid.     If  a  residue  remains,  this  must  be  tested  for  BEN- 
ZOIC  ACID  by  heating.     Carbonate  of  potash  in  excess  is 
then  added  to  the  hydrochloric   solution,  and  the  latter 
boiled  for  some  time  and  filtered.     The  alkaline  nitrate 
contains  the  organic  acid,  under  all  circumstances.     This 
filtered  solution  is  therefore  exactly  saturated  with  hydro- 
chloric acid,  and  the  fluid  tested,  as  directed  §  109.     No 
regard  need  be  had  to  formic  acid,  all  the  formiates  being 
soluble  in  water. 

2.  ACETIC  ACID  is  most  readily  detected  in  such  com- 
pounds by  means  of  sulphuric  acid  and  alcohol.  (§  104,  a.) 

Compounds  which  are  supposed  to  consist  of  but  one  acid 
and  one  base,  $*c- 

C.  SUBSTANCES  INSOLUBLE  OR  SPARINGLY  SOLUBLE  IN  WATER, 

HYDROCHLORIC  ACID,  NITRIC  ACID,  AND  AQUA  REGIA. 

DETECTION   OF    THE  BASE   AND    THE   ACID. 

§  113, 

Under  this  head  we  propose  to  consider  SULPHATE  OP 

BARYTES,    SULPHATE    OF    STRONTUN,    SULPHATE    OF    LIME, 


DETECTION  Otf  THE  BASE  AND  ACID.  209 

SILICA,  SULPHATE  OF  LEAD,  CHLORIDE  OF  LEAD,  and  CHLO- 
RIDE OF  SILVER,  as  the  most  frequently  occurring  com- 
pounds belonging  to  this  class.  For  the  less  frequently 
occurring  compounds  of  this  kind,  we  refer  to  §  127. 

Sulphate  of  lime  and  chloride  of  lead  are  not  altogether 
insoluble  in  water,  and  sulphate  of  lead  may  be  dissolved 
in  hydrochloric  acid.  As  these  compounds  are,  however, 
so  sparingly  soluble  that  we  seldom  can  effect  their  com- 
plete solution,  we  mention  them  here  once  more,  in  order 
that  they  may  be  detected  by  the  method  laid  down  in 
this  section,  should  they  have  escaped  detection  in  the 
examination  of  their  aqueous  or  acid  solutions. 

1.  A  very  minute  quantity  of  the  substance  under  exam- 
ination is  treated  with  hydrosulphuret  of  ammonia. 

a.  IT  BECOMES  BLACK  ;  this  indicates  the  presence 

of  a   SALT  OF  LEAD  Or  CHLORIDE  OF  SILVER.       A  SOmC- 

what  larger  portion  of  the  substance  is  then  digested 
for  some  time  with  hydrosulphuret  of  ammonia.  In 
this  process  the  metallic  salt  becomes  decomposed, 
and  a  sulphuret  is  formed,  which  remains  undissolved> 
whilst  we  have  in  solution  the  acid  of  the  metallic 
salt  combined  with  the  ammonia  of  the  hydrosul- 
phuret of  ammonia.  The  solution  is  then  filtered,  the 
undissolved  sulphuret  washed  and  dissolved  in  nitric 
acid,  and  this  nitric  solution  tested,  with  sulphuric 
acid,  for  lead  ;  and  with  hydrochloric  acid,  and  sub- 
sequent addition  of  ammonia,  for  SILVER.  One  portion 
of  the  filtered  liquid  is  tested  for  SULPHURIC  ACID,  with 
chloride  of  barium,  after  having  previously  decom- 
posed the  excess  of  the  hydrosulphuret  of  ammonia, 
by  the  addition  of  hydrochloric  acid  and  boiling  up  ; 
another  portion  is  tested  for  HYDROCHLORIC  ACID,  with 
solution  of  silver ;  after  having  previously  acidified 
the  liquid  with  nitric  acid,  and  then  boiled  it. 

b.  IT  BECOMES  WHITE.     Absence  of  a  heavy  me- 
tallic oxide.     A  small  portion  of  the  substance  under 
examination  is  reduced  to  a  very  fine  powder,  and 
then  mixed  with  four  times  its  quantity  of  carbonate 
of  soda  and  potash,  put  into  a  small  platinum  crucible, 
and  fused  over  a  Berzelius  spirit-lamp.     The  fused 
mass  is  boiled  with  water. 


210  DETECTION  OF  THE  BASES. 

*>.  Complete  solution  takes  place  :  SILICA.  We 
assure  ourselves  of  the  presence  of  this  substance 
by  supersaturating  the  solution  with  hydrochloric 
acid,  and  evaporating  to  dryness.  In  this  operation, 
silicic  acid  is  converted  from  its  soluble  into  its 
insoluble  modification.  It  remains,  therefore,  un- 
dissolved  on  treating  the  residue  with  water.  When 
mixed  with  carbonate  of  soda,  and  exposed  to  a 
strong  blow-pipe  flame,  a  transparent  glass  is  pro- 
duced. (§  99,  b  ) 

/3.  A  white  residue  remains  ;  this  indicates  one 

of  the  SULPHATES  OF  THE  ALKALINJE  EARTHS.       The 

solution  is  filtered,  and  the  filtered  liquid  acidified 
with  hydrochloric  acid,  and  then  tested  for  SULPHU- 
RIC ACID,  with  chloride  of  barium.  The  white 
residue  (which  contains  the  alkaline  earth  as  a 
carbonate)  is  carefully  washed,  dissolved  in  a  small 
quantity  of  dilute  sulphuric  acid,  and  the  solution 
tested  for  BARYTES,  STRONTIAN,  or  LIME,  as  directed 
§  107,  4. 

Compounds  in  which  all  the  more  frequently  occurring 
Bases,  Acids,  Metals,  and  Metalloids,  are  supposed  to 
•     be  present. 

A.  SUBSTANCES  BOTH    SOLUBLE  AND  INSOLUBLE  IN  WATER, 

AND  SOLUBLE  IN  HYDROCHLORIC  ACID  OR  NITRIC  ACID. 

Detection  of  the  bases* 
§  114. 

In  this  scheme  for  the  testing  of  the  bases  we  have 
united  the  compounds  belonging  to  classes  I.  and  II., 
(vide  §  106,)  since  the  method  of  detection  is  in  most  cases 
the  same  for  both  classes.  Those  parts  which  refer  only 
to  substances  insoluble  in  water,  and  soluble  in  hydrochlo- 
ric acid  and  nitric  acid,  are  enclosed  between  inverted 


*  The  arsenious  and  arsenic  acid,  and  several  salts,  have  here  been 
had  regard  to,  since  we  are,  in  this  course  of  examination,  led  to  their 
detection. 


SUBSTANCES  SOLUBLE  IN  ACIDS.          211 

trommas,  (" "),  and  may,  therefore,  be  passed  over 

unnoticed,  when  examining  substances  soluble  in  water. 

I.  THE  SOLUTION  is  AQUEOUS, 

A  small  quantity  of  hydrochloric  acid  is  added. 
1.  THE   SOLUTION  HAD  AN   ACID  OR   NEUTRAL    REACTION 
PREVIOUS  TO  THE  ADDITION  OF  THE  HYDROCHLORIC  ACID. 

a.  No  PRECIPITATE  is  FORMED  :  this  indicates  the 
absence  of  silver  and  protoxide  of  mercury.     Pass 
over  to  §  115. 

b.  A  PRECIPITATE  is  FORMED;  hydrochloric  acid 
is  added  to  the  solution  drop  by  drop,  as  long  as  the 
quantity  of  the  precipitate  increases.     This  precipi- 
tate may  consist  of  chloride  of  silver,  protochloride  of 
mercury,  chloride  of  lead,  or  a  basic  salt  of  antimony, 
or,  possibly,  also  of  benzoic  acid.     The  fluid  is  agi- 
tated, and  a  portion  of  it,  together  with  the  therein 
suspended  particles  of  the  precipitate,  mixed  with  a 
large  quantity  of  water,  and  heated  to  boiling.     If 
compounds  of  antimony,  bismuth,  or  tin  are  present, 
the  dilution  with  water  may  render  the  liquid  turbid, 
which  phenomenon  is  usually  distinctly  perceived, 
notwithstanding  the  precipitate  which  the  fluid  already 
contained  previous  to  the  addition  of  the  water.     In 
order  to  judge  with  certainty,  whether  the  precipitate 
produced  by  hydrochloric  acid  redissolves  in  the  wa- 
ter  on  boiling   or  not,   and,  therefore,  whether  the 
further  operation  is  to  be  conducted  according  to  *>  or 
£,  hydrochloric  acid  is  added  to  the  dilute  solution — 
{previous  to  heating) — till  the  milkiness   has  com- 
pletely vanished. 

«  The  precipitate  vanishes  ;  this  indicates  the  ab- 
sence of  silver  and  protoxide  of  mercury.  The  ori- 
ginal solution,  together  with  the  precipitate  produced 
in  it  by  hydrochloric  acid  is  heated  to  boiling  and 
filtered  hot.  Should  the  precipitate  not  completely 
redissolve,  the  residue  is  once  more  boiled  with  water, 
and  the  solution  filtered  hot  into  the  first  filtrate. 
The  filtered  solution  is  treated  as  directed  §  115. 
Should  it  have  deposited  a  precipitate,  or  small  crys- 
tals .{chloride  of  lead)  have  formed  on  cooling,  it  must 


212  DETECTION    OF    THE    BASES. 

be  previously  heated,  till  it  appears  transparent  again. 

/3.   The  precipitate  does  not  vanish,  at   least  not 

completely  ;  this  indicates  the  presence  of  SILVER  or 

PROTOXIDE  OF   MERCURY. 

The  original  solution  (with  the  hydrochloric  acid)  is 
treated  as  directed  §  114,  I.  1,  b,  «*  The  residuary  inso- 
luble precipitate  is  washed  and  tested  as  follows  :  it  is,  if 
possible,  removed  from  the  filter  and  treated  with  ammo- 
nia, in  a  small  tube.  If  it  dissolves  in  this  substance,  it 
consists  exclusively  of  SILVER  ;  if  it  becomes  black,  PROT- 
OXIDE OF  MERCURY  is  present.  In  this  case,  or  whenever 
a  residue  insoluble  in  ammonia  remains,  this  must  be  fil- 
tered off,  and  nitric  acid  in  excess  added  to  the  filtered 
liquid  ;  the  formation  of  a  white,  curdy  precipitate  indi- 
cates SILVER. 

2.  THE  AQUEOUS  SOLUTION  HAI>  AN  ALKALINE  REACTION. 

fl.  No  EVOLUTION  OF  GAS  TAKES  PLACE  AND  NO  PRE- 
CIPITATE IS  FORMED,  ON  THE  ADDITION  OF  HYDROCHLO- 
RIC ACID,  OR,  A  PRECIPITATE  IS  AT  FIRST  FORMED,  BUT 
REDISSOLVES  ON  THE  FURTHER  ADDITION  OF  HYDRO- 
CHLORIC ACID;  pass  over  to  §  115.  For  all  that 
relates  to  substances  belonging  to  the  second  class — 
(i.  e.  those  insoluble  in  water,  and  soluble  in  hydro- 
chloric acid  or  nitric  acid) — enclosed  between  in- 
verted commas,  look  to  the  passages  upon  phosphate 
of  alumina,  but,  if  an  ammoniacal  salt  is  present, 
also  to  those  upon  the  oxalates  of  the  alkaline  earlhs? 
since  the  solution  of  these  compounds  in  a  fluid  with 
alkaline  reaction  is  not  impossible. 

b.  A  PRECIPITATE  IS  FORMED,  ON  THE  ADDITION  OF 
HYDROCHLORIC  ACID,  WHICH  DOES  NOT  REDISSOLVE  IN 
AN  EXCESS  OF  THE  PRECIPITANT. 

<*.  The  precipitate  is  formed  without  simulta- 
neous evolution  of  sulphuretted  hydrogen  gas.  A 
portion  of  the  fluid  with  the  precipitate  suspended 
therein,  is  diluted  with  a  large  proportion  of  water, 
and  heated.  The  solution  of  the  precipitate  is 
indicative  of  LEAD,  or  possibly  also  of  benzoic  acid. 
The  original  solution  is  then  heated  to  boiling,  toge- 
ther with  the  precipitate  produced  by  hydrochloric 
acid,  filtered  hot,  and  the  residue  (if  any  remain) 
boiled  with  water  and  filtered  hot  into  the  hydro- 


DETECTION    OF    THE    BASES.  213 

chloric  solution.  The  filtrate  is  treated  according 
to  §  115;  should  it  become  turbid  on  cooling,  it 
must  be  heated  again  previous  to  being  further 
tested.  If  the  precipitate  does  not  redissolve  on 
heating  the  fluid  diluted  with  water,  but  is  dis- 
solved by  ammonia,  SILVER  is  present.  The  ori- 
ginal solution  is  treated  in  the  same  manner  as  if 
the  precipitate  had  been  redissolved. 

/3.   The  precipitate  is  formed  with  simultaneous 
evolutions  of  sulphuretted  hydrogen  gas. 

aa.  The  precipitate  is  of  a  pure  white  colour, 
and  consists  of  sulphur.  In  this  case  an  alka- 
line bisulphuret  is  present.  Filter  the  solution 
and  pass  over  to  §  118,  bearing  in  mind  that  of 
the  substances  considered  §  118,  oxide  of  chro- 
mium and  alumina  alone  can  be  present. 

bb.  The  precipitate  is  coloured.  In  this  case 
we  must  suppose  that  a  metallic  sulphur  salt  is 
present,  i.  e.  a  combination  of  an  alkaline  sul- 
phur base  with  an  electro-negative  sulphuret. 
The  solution  is  heated  to  boiling  and  filtered  ; 
the  nitrate  is  further  tested  as  stated  under  aa. 
The  precipitate  is  treated  as  §116  directs;  it 
may  consist  of  SULPHURET  OF  GOLD,  SULPHURET 

OF    PLATINUM,  SULPHURET    OF    TIN,    SULPHURET    OF 
ARSENIC,  OR  SULPHURET  OF  ANTIMONY. 
C.      No     LASTING    PRECIPITATE     IS     FORMED,     ON     THE 

ADDITION    OF     HYDROCHLORIC    ACID,    BUT    EVOLUTION  OF 

GAS   TAKES  PLACE. 

*.  The  escaping  gas  has  the  odour  of  sulphuret- 
ted hydrogen;  this  indicates  a  simple  alkaline 
sulphur  compound.  The  further  operations  are 
conducted  as  directed  aa. 

/3.  The  escaping  gas  emits  no  odour ;  in  this 
case  it  is  carbonic  acid  which  was  combined  with 
an  alkali.  Pass  over  to  §  115,  bearing  in  mind, 
that  mercury,  bismuth,  insoluble  salts  of  magnesia, 
and  (if  the  reaction  is  strongly  alkaline)  barytes, 
strontian,  and  lime  cannot  be  present,  or  at  least 
only  under  very  peculiar  circumstances,  (e.  g. 
mercury  as  a  cyanide.) 
9* 


214  DETECTION  OF  THE  BASES. 

II.  THE  SOLUTION  is  HYDROCHLORIC. 
It  is  treated  as  §  115  directs. 

III.  THE  SOLUTION  is  NITRIC. 

A  small  portion  of  it  is  diluted  with  much  water. 

1.  IT  REMAINS  TRANSPARENT  ;  add  hydrochloric  acid. 

a.  No  precipitate  is  formed.    Absence   of  silver. 
The  original  solution  is  treated  according  to  §  115. 

b.  A  precipitate  is  formed.     If  it  does  not  redis- 
solve  on  heating  the  fluid,  but  is  dissolved  by  ammo- 
nia, after  washing,  SILVER  iV  present.     The  original 
solution  is  treated  as  staled  §1 15. 

2.  THE  SOLUTION  BECOMES  TURBID  AND  MILKY:  BISMUTH 
or  ANTIMONY.     The  fluid  is  filtered,  and  the  filtrate  tested 
for  silver  according  to  §  114,  III.  1  ;  the  original  solution 
is  tested  as  §  115  directs. 

§  H5. 

Solution  of  sulphuretted  hydrogen  is  added  to  a  SMALL 
PORTION  of  the  transparent  acid  solution,  till  the  fluid,  after 
agitation,  and  application  of  heat,  emits  a  clearly  percep- 
tible odour  of  sulphuretted  hydrogen. 

a.  No  PRECIPITATE  is  FORMED,  not  even  after  the 
lapse  of  some  time.     Pass  over  to  §  118,  for  neither 
lead,  bismuth,  cadmium,  copper,  mercury,  gold,  pla- 
tinum, antimony,  tin,  nor  arsenic,*  are  present ;  the 
absence  of  peroxide  of  iron  and^  of  chromic  acid  is 
also  indicated  by  this  negative  reaction. 

b.  A  PRECIPITATE    IS  FORMED. 

aa.  It  is  of  a  pure  white  colour,  thin,  in  the  form 
of  a  fine  powder,  and  does  not  vanish  on  the  addi- 
tion of  hydrochloric  acid.  It  consists  of  sulphur, 
and  indicates  PEROXIDE  OF  IRON.!  None  of  the 


*  To  assure  ourselves  of  the  certain  absence  of  arsenic  acid,  we  must 
allow  the  test  solution  to  stand  for  some  time,  or  add  sulphurous  acid, 
previous  to  the  addition  of  the  sulphuretted  hydrogen.  (Compare  §  93,  g.) 

t  Sulphur  is  also  precipitated  in  presence  of  sulphurous  acid,  iodic  acid, 
bromic  acid, — which  substances  we  do  not  treat  of  in  the  present  work, — 
and  also  when  chromic  acid,  chloric  acid,  or  free  chlorine  are  present. 


DETECTION  OF  THE    BASES.  215 

other  metals,  enumerated  at  §  115,  a,  can  be  pre- 
sent. The  original  solution  is  treated  as  §  118 
directs. 

bb.   The  precipitate  is  coloured. 

Solution  of  sulphuretted  hydrogen  is  added  to 
the  larger  portion  of  the  acid  or  acidified  solution, 
till  the  latter  has  acquired  the  distinct  odour  of 
sulphuretted  hydrogen,  and  the  precipitate  no  longer 
increases  on  the  continued  addition  of  the  reagent ; 
the  solution  is  then  heated  to  boiling,  and  strongly 
agitated  for  some  time* 

In  many  cases,  and  especially  when  there  is  any 
reason  to  suppose  arsenic  to  be  present,  it  isdbetter 
to  transmit  sulphuretted  hydrogen  gas  through  the 
solution, 

1.  THE    PRECIPITATE    IS    OF    A     PURE    YELLOW    COLOUR. 

In  this  case  it  can  consist  only  of  ARSENIOUS  or  ARSENIC 

ACID,  Of  PEROXIDE    OF    TIN,  Or  of  OXIDE  OF  CADMIUM.    The 

fluid— (which  is  then  further  to  be  tested  according  to 
§  1 1 8) — is  separated  from  the  precipitate,*  and  the  latter 
washed  and  drenched  with  ammonia. 

a.  The  precipitate  is  completely  redissolved  :  ab- 
sence of  cadmium.     Acetic  acid  is  added  slightly  in 
excess  to  the  solution,  and  the  precipitate  formed  is 
tested  for  TIN  and  ARSENIC,  as  §  116,  1,  directs. 

b.  A  yellow  residue  remains,  even  after  a  further 
addition  of  ammonia  and  the  application  of  a  mo- 
derate  heat :    CADMIUM.     The  solution   is    filtered, 
and  acetic  acid,  slightly  in  excess,  added  to  the  filtrate. 
If  no  precipitate  is  formed,  the  first  precipitate  con- 
sisted exclusively  of  sulphuret  of  cadmium  ;  but  if  a 
precipitate  is  formed,  it  denotes  the  presence  of  PE- 
ROXIDE OF  TIN,  or  ARSENIC;  this  precipitate  is  tested 
as  directed  §  116,  1. 

2.  THE      PRECIPITATE     IS     ORANGE-RED,      OR     YELLOW, 
WITH    A    SHADE      OF     ORANGE-COLOUR.       It    indicates  ANTI- 
MONY, but   may,  morover,   contain   TIN— (should  it  have 

*  The  best  method  of  separating  a  precipitate  from  a  fluid,  is  to 
allow  the  precipitate  to  settle — (this  is  facilitated  by  heating  and 
agitating) — the  fluid  may  then  be  decanted  and  the  precipitate 
washed, 


216  DETECTION    OF   THE    BASES. 

been  present  as  a  peroxide) — ARSENIC  or  CADMIUM  ;  the 
precipitate  is  separated  from  the  fluid — (which  is  tested 
as  §  118  directs) — washed,  and  a  small  portion  of  it  di- 
gested with  hydrosulphuret  of  ammonia,  which  contains 
sulphur  in  excess. 

a.  It  redissolves  completely  :  absence  of  cadmium. 
The  rest  of  the  precipitate  is  treated   as   directed  $ 
116,2. 

b.  A  yellow  residue  remains,  even  after  a  more 
protracted  digestion,  with  a  larger  quantity  of  hydro- 
sulphuret of  ammonia  :    CADMIUM.     The  entire  pre- 
cipitate is  then  treated  in  the  same  manner  as  the 
^>ecimen,  the  fluid  filtered  off  from  the  sufphuret  of 
cadmium,  and  acetic  acid  in  a  slight  excess  added  to 
the  filtrate  ;  the  precipitate  formed  is  treated  as  §  1 16, 
2,  directs. 

3.  THE  PRECIPITATE  is  or  A  DARK  BROWN  OR  BLACK 
COLOUR.  The  precipitate  is  separated  from  the  fluid — 
(which  is  then  tested  as  §  118  directs) — washed  with 
water,  drenched  and  digested  for  some  time,  with  hydro- 
sulphuret of  ammonia,  containing  sulphur  in  excess.* 

a.  The  precipitate  is  completely    redissolved  in 
hydrosulphuret  of  ammonia,  or  in  sulphur et  of  po- 
tassium ;  absence  of  cadmium,  lead,  bismuth,  copper, 
and  mercury:  §  117  may, therefore,  be  passed  over 
unnoticed.     The  solution  is  diluted,  and  acetic  acid 
added,  till  an  acid  reaction  becomes  manifest ;  it  is 
then  heated  to  boiling,  and  the   precipitate  formed, 
treated  as  §  116  directs. 

b.  It  does  not  dissolve,  or  at  least  not  completely. 
The  fluid  is  filtered  off  from  the  precipitate,  and  the 
latter  is  washed,  (in  case  §  115,  3  b  «,)  or  (in  case  ft) 
once  more  digested  with  hydrosulphuret  of  ammonia, 
filtered  into  the  first  solution,  and  then  washed.    The 
residue  is   reserved  for  further  examination,  as  di- 
rected §  117.     A  small  portion  of  the  filtrate  contain- 

*  If  the  solution  contains  copper,  which  may  generally  be  detected  by 
its  colour,  but  with  certainty  by  testing  with  a  clean  iron  rod,  (vide  §  91, 
i,  6,)  solution  of  sulphuret  of  potassium  must  be  substituted  for  hydrosul- 
phuret  of  ammonia,  and  the  sulphur  precipitate  be  boiled  in  it,  (i.  e.  in  tho 
sulphuret  of  potassium,)  vide  §  91,  £,  2. 


DETECTION    OF    THE    BASES.  217 

ing  hydrosulphuret  of  ammonia  is  diluted  with  from 
three  to  four  parts  of  water,  acetic  acid  added,  till  an 
acid  reaction  becomes  manifest,  and  the  liquid  heated 
to  boiling. 

«*.  The  fluid  simply  becomes  milky,  owing  to  the 
separation  of  sulphur.  Absence  of  gold,  platinum, 
tin,  antimony,  and  arsenic.  Pass  over  to  §  117. 

£.  A  coloured  precipitate  is  formed.  The  colour 
of  the  precipitate  is  minutely  inspected ;  the  entire 
solution  containing  the  hydrosulphuret  of  ammonia  is 
then  slightly  diluted,  acetic  acid  added,  till  an  acid 
reaction  becomes  manifest,  and  the  fluid  heated  to 
boiling. 

§   116. 

The  precipitate  which  acetic  acid  has  produced  in  the 
solution  containing  hydrosulphuret  of  ammonia  or  sul- 
phuret  of  potassium,  is 

1.  OF  A  PURE  YELLOW  COLOUR,  WITHOUT  THE  SLIGHT- 
EST SHADE  OF  ORANGE  :  ARSENIC  or  TIN.  The  solution  is 
filtered  off  from  the  precipitate,  the  latter  well  washed,  and 
together  with  the  filter  placed  between  some  sheets  of 
blotting-paper  ;  when  the  paper  has  imbibed  the  greater 
part  of  the  water,  the  still  moist  precipitate  is  removed 
from  the  filter,  and  mixed  in  a  small  porcelain  crucible 
with  about  half  its  amount  of  pure  anhydrous  carbonate  of 
soda,  and  one  and  a-half  its  amount  of  pure  nitre ;  the 
mass  is  then  gently  heated,  and  stirred,  till  it  has  be- 
come completely  dry,  when  a  stronger  heat  is  applied — 
(beginning  at  the  edge  of  the  crucible) — till  the  entire  mass 
fuses,  and  every  particle  of  the  sulphuret  is  decomposed. 
(If  after  drying  the  mass  a  very  high  degree  of  heat  is 
suddenly  applied  and  allowed  to  act  upon  the  whole  cruci- 
ble at  once,  slight  explosions  take  place,  whereby  more  or 
less  of  the  mass  is  thrown  out  of  the  crucible.) 

a.  The  melting  mass  is  transparent.  Absence  of 
tin.  The  mass,  after  cooling,  is  boiled  with  water, 
the  solution  divided  into  two  portions,  and  very  dilute 
nitric  acid  very  cautiously  added  to  the  one,  till  a 
feebly  acid  reaction  becomes  manifest ;  heat  is  then 


218  DETECTION    OF    THE    BASES. 

applied.  (If  there  is  really  no  tin  present,  no  white 
pulverulent  residue  must  remain,  on  boiling  the  de- 
flagrated mass  with  water,  neither  must  any  precipi- 
tate be  formed,  on  acidulating  the  solution  with  nitric 
acid,  not  even  after  standing  at  rest  for  some  time.) 
Nitrate  of  silver  is  added  to  the  acidified  solution,  after 
cooling,  and  the  fluid  filtered ;  if  any  traces  of  chloride 
of  silver  should  still  separate,  which  is  frequently  the 
case  if  the  reagents  are  not  absolutely  pure,  or  the  pre- 
cipitate not  completely  washed.  The  filtrate  is  then 
slowly  and  cautiously  covered  in  a  test-tube  with  very 
dilute  ammonia — (one  part  of  ammonia  to  twenty  parts 
of  water— and  allowed  to  stand  for  some  time,  without 
agitating.  The  formation  of  a  reddish  brown  precipi- 
tate, which  appears  like  a  cloud  between  the  two 
layers  (of  the  test  .specimen  and  the  dilute  ammonia,) 
indicates  ARSENIC  ;  (this  precipitate  is  more  clearly 
seen,  on  the  light  falling  upon  than  through  it.)  As 
a  further  proof,  the  second  portion  of  the  solution  of 
the  deflagrated  mass  is  precipitated  by  solution  of 
neutral  acetate  of  lead,  the  precipitate  filtered  off, 
dried  between  some  sheets  of  blotting-paper,  and 
then,  on  charcoal,  exposed  to  the  reducing  flame  of 
the  blow-pipe.  If  arsenic  is  really  present,  a  grain 
of  metallic  lead  containing  arsenic  will  be  obtained, 
which  emits  the  garlic  odour  of  arsenic  very  long  and 
continuously ;  as  often  as  it  is  exposed  to  the  reducing 
blow-pipe  flame.  For  further  confirmation,  the  arsenic 
must  be  obtained  in  its  metallic  state.  (Compare  §  94, 
d  and  (&.)  Whether  the  arsenic  was  present  in  the 
compound  under  examination  as  arsenic  acid,  or  as 
arsenious  acid,  may  be  ascertained  according  to  the 
method  described  at  the  end  of  §  94. 

b.  The  melting  mass  is  milky  and  turbid.  This 
is  a  probable  indication  of  the  presence  of  tin.  The 
mass  is  digested  with  cold  water,  and  rubbed  with  it 
in  a  mortar  j  the  solution  is  then  filtered,  and  the  pre- 
cipitate which  remains,  if  tin  is  really  present,  very 
carefully  washed,  and  then  tested  for  tin,  by  reducing 
it  before  the  blow-pipe  mixed  with  cyanide  of  potas- 
sium and  carbonate  of  soda,  and  strongly  rubbing  the 


DETECTION    OF    THE    BASES.  219 

specimen  in  a  mortar,  with  the  addition  of  water;  vide 
§  94,  b.     The  liquid  filtered  off  from  this  precipitate 
is  divided  into  two  portions  and  tested  for  arsenic  as 
§  116,  1,  a,  directs.     A  slight  precipitate  generally 
separates  on  acidifying  the  solution  with  nitric  acid. 
This  may  be  filtered  off  and  tested  for  tin  in  the  same 
manner  as  the  undissolved  residue,  (vide  supra.)  But 
if  the  tin  has  already  been  detected,  this  precipitate 
may  be  left  in  the  solution,  nitrate  of  silver  added, 
filtered,  and  the  fluid  tested  for  arsenic  acid,  as  directed 
above.     Whether  the  tin  was  present  as  protoxide,  is 
ascertained,  by  mixing  a  portion  of  the  original  solu- 
tion in  water  or  hydrochloric  acid,  with  a  drop  of  nitric 
acid  and  some  chloride  of  gold.     (§  94,  b,  5.) 
2.    ORANGE-RED,    OR   YELLOW,  WITH  A  SHADE  OF  OR- 
ANGE; ANTIMONY;  and  besides  TIN  and  ARSENIC  may  be 
present.     The  precipitate  is  washed  and  fused  with  nitre 
and  carbonate  of  soda,  in  short,  tested  for  arsenic  and  prot- 
oxide of  tin,  exactly  as  §  116,  1,  6,  directs.     The  residue 
remaining    on  treating   the   deflagrated    mass    with   cold 
water,  as  well  as  the  precipitate  which  may  perchance  be 
formed  un  acidifying  the  solution  with  nitric  acid,  may  be 
tested  in  three  different  ways. 

a.  The  residue  (or  precipitate)  is  most  carefully 
washed,  mixed  with  cyanide  of  potassium  and  carbon- 
ate of  soda,  and  exposed  on  charcoal,  to  the  reducing 
flame  of  the  blow-pipe. 

«.  Metallic  globules  appear,  which  at  last  com- 
pletely volatilize,  with  the  emission  of  white  fumes 
and  the  formation  of  a  white  crust.  This  is  con- 
firmatory of  the  presence  of  ANTIMONY,  and  of  the 
absence  of  tin. 

/3.  White  metallic  globules  remain,  after  long 
blowing :  TIN.  Their  presence  and  nature  may 
best  be  ascertained  by  rubbing  the  particles  of  the 
charcoal  surrounding  the  test-specimen,  together 
with  the  latter,  in  a  mortar  with  some  water. 
(§  94,  6.) 

b.  The  residue  (or  precipitate)  is  very  carefully 
washed  with  water,  dried,  and  fused  for  some  time  in 
a  small  porcelain  crucible,  together  with  from  four  to 


220  DETECTION    OF    THE    BASES. 

five  times  its  amount  of  cyanide  of  potassium.  The 
mass,  after  cooling,  is  drenched  with  water  heated  to 
boiling,  and  thus  the  dross  is  separated  from  the  metal- 
lic globules.  These  are  treated  with  nitric  acid,  and 
the  operation  for  the  detection  of  tin  and  antimony 
conducted  exactly  as  §  106  B,  2,  6,  directs. 

c.  The  residue  (or  precipitate)  is  well  washed,  dis- 
solved in  hydrochloric  acid,  the  solution  diluted,  and  a 
small  zinc  rod  placed  into  it.  When  the  action  of  the 
latter  has  ceased,  and  the  reduction  is  complete,  the 
reduced  metals  (which  can  be  easily  separated  from 
the  compact  piece  of  zinc,)  are  boiled  with  nitric  acid, 
and  the  operation  is  carried  on  exactly  as  §  106  B,  2, 
bj  directs. 

The  two  latter  methods  of  distinguishing  tin  and 
antimony  from  each  other,  when  together  in  the  same 
substance,  are  for  beginners  at  least,  far  safer  than 
the  first. 

3.  BROWNISH-BLACK;  GOLD  or  PLATINUM  ;  besides,  per- 
haps, also  ANTIMONY,  ARSENIC,  TIN.  Add  to  the  original 
solution  of  the  substance. 

a.  Protochloride  of  tin  ;  the  formation  of  a  reddish- 
brown  or  purple  red  precipitate  denotes  GOLD.    We 
assure  ourselves  of  the  presence  of  this  metal  by  test- 
ing the    original  solution  wilh  protosulphate  of  iron, 
whereby  metallic  gold  is  precipitated  as  a  black  pow- 
der. 

b.  Muriate  of  ammonia  ;  the  formation  of  a  yellow 
precipitate  is  indicative  of  the  presence  of  PLATINUM. 
The  solution,  if  highly  dilute,  should  be  concentrated 
by  evaporation,  previous  to  adding  this  reagent. 

A  portion  of  the  precipitate  is  tested  for  ARSENIC,  as 
directed  §  116,  1.  The  rest  is  boiled  with  hydrochlo- 
ric acid  and  filtered  off;  the  filtrate  is  tested  for  ANTI- 
MONY by  dropping  one  drop  of  it  into  water;  (after 
having  previously  removed,  as  much  as  possible,  the 
excess  of  acid  by  evaporation  ;  if  the  water  becomes 
turbid  and  milky,  antimony  is  present.  Or  a  small 
portion  of  the  filtrate  is  mixed  with  solution  of  sulphu- 
retted hydrogen  ;  the  formation  of  an  orange-coloured 
precipitate  indicates  antimony.  The  rest  of  the  hy- 
drochloric solution  is  evaporated  to  dryness,  mixed 


DETECTION    OF   THE    BASES.  221 

with  carbonate  of  soda  and  cyanide  of  potassium,  and 
tested  for  peroxide  of  tin,  as  §  1 16,  2,  directs.  Anti- 
mony and  tin  may,  however,  more  safely  be  detected 
by  precipitating  them  from  the  hydrochloric  filtrate, 
by  means  of  zinc  ;  in  fact,  by  treating  exactly  as  §  1 1 6, 
2,  c,  directs. 

§  117. 

The  precipitate  which  has  not  been  dissolved  by  hydro- 
sulphuret  of  ammonia,  is  washed,  and  then  boiled  with 
nitric  acid.  This  may  best  be  done  in  a  small  porcelain 
basin,  constantly  stirring  with  a  glass  rod. 

1.  THE  PRECIPITATE  DISSOLVES,  AND  NOTHING  REMAINS 
FLOATING  IN  THE  FLUID  EXCEPT  THE  SEPARATED  LIGHT, 

FLOCCULENT  YELLOW  SULPHUR  ]  this  indicates  the  absence 
of  mercury.  CADMIUM,  COPPER,  LEAD,  and  BISMUTH,  may 
be  present.  If  the  precipitate  was  of  a  pure  yellow  colour, 
it  consisted  of  CADMIUM  alone  ;  if  it  was  brown  or  black, 
it  must  be  filtered  off  from  the  separated  sulphur,  and  the 
filtrate  tested  as  follows. 

a.  Ammonia  in  excess  is  added  to  one  portion  of 
the  filtrate. 

«,  No  precipitate  is  formed,  or  the  precipitate 
formed  at  first,  redissolves  completely  in  an  excess 
of  the  precipitant.  Absence  of  lead  and  bismuth* 
The  solution  is  treated  as  §  117,  1,  6,  directs,  bear- 
ing in  mind  §  117,  1,  a,  y. 

/3.  A  lasting  precipitate  is  formed  :  LEAD  or 
BISMUTH.  The  liquid  is  filtered  off,  and  the  filtrate 
treated  according  to  §  1 1 7,  1 ,  6,  bearing  in  mind 
§117,  l,c,  y. 

•y.  The  fluid  is  blue-coloured;  no  matter  whether 
a  precipitate  is  formed  or  not ;  COPPER. 

b.  Hydrochloric  acid  is  added  to  the  ammoniacal 
solution  till  a  slightly  acid  reaction  becomes  manifest ; 
carbonate  of  ammonia  is  then  added  in  excess. 

«.  The  fluid  remains  clear :  absence  of  cad- 
mium- 

/3.  A  white  precipitate  is  formed  immediately, 
or  after  applying  heat  to  the  solution  :  CADMIUM. 
We  assure  ourselves  of  the  presence  of  this  sub- 


222  DETECTION    OP    THE    BASES. 

stance  by  filtering  the  fluid  off  from  the  precipitate, 
washing  the  latter,  dissolving  it  in  hydrochloric 
acid,  and  adding  solution  of  sulphuretted  hydro- 
gen. A  yellow  precipitate  must  appear,  if  cad- 
mium is  present. 

Should  copper  not  yet  have  been  indicated  by  a 
blue  colouring  of  the  ammoniacal  solution,  the  fluid 
in  which  carbonate  of  ammonia  has  produced  no  pre- 
cipitate, (§117,  1,  b,  *,)  or  the  filtrate  of  §  1  17,  1,  6,  /a, 
must  be  further  and  more  minutely  examined,  by 
slightly  acidifying  the  one  or  the  other  with  acetic 


acid,  and  adding  ferrocyanide  of  potassium.     If  cop- 
per is  present 
be  produced. 


er  is  present,  a  brownish-red  precipitate  or  tint  will 


c.  In  the  case  of  §  117,  1,  a,  /3,  a  not  too  incon- 
siderable quantity  of  sulphuric  acid  is    added  to  a 
second  portion  of  the  solution  of  the  sulphurets  in 
nitric  acid  :  the"  formation  of  a  precipitate  is  indica- 
tive of  the  presence  of  LEAD.      This  reaction  may 
be  rendered  more  obvious  and  distinct  by  expelling 
the  greater  part  of  the  free  nitric  acid  by  evaporation. 

d.  The  rest  of  the  solution  (in  the  case  of  §  117, 
1,  a,  £,)  is  evaporated  to  dryness,   a  few  drops  of 
water  added,  and,  in  proportion  to  the  quantity,  one 
or   two   drops  of  hydrochloric    acid,   and  the   fluid 
heated.     The  solution  is  then  poured  into  a  test-tube 
containing  water  ;  if  the  water  becomes  turbid  and 
milky,  BISMUTH  is  present.* 

2.  THE  PRECIPITATE  OF  THE  SULPHURETS  DOES  NOT 
COMPLETELY  REDISSOLVE  IN  THE  BOILING  NITRIC  ACID, 
AND  A  PRECIPITATE  REMAINS,  BESIDES  THE  LIGHT  FLOC- 

CULENT  SULPHUR.  This  indicates  PEROXIDE  OF  MER- 
CURY, with  a  certain  degree  of  probability,  (and  almost 
with  certainty,  if  the  precipitate  is  heavy  and  black.)  The 
precipitate  is  allowed  to  settle,  and  the  fluid  filtered  off 
from  it  ;  this  filtrate  must  be  tested  for  CADMIUM,  COPPER, 
LEAD,  and  BISMUTH,  by  mixing  a  small  portion  of  it  with  a 
large  volume  of  solution  of  sulphuretted  hydrogen,  and  if  a 

We  refer  to  chapter  TL  (additions  and  remarks  to  §  117)  for  another 
method  of  distinguishing  cadmium,  copper,  lead,  and  bismuth,  from  each 
other 


DETECTION    OF  THE    BASES.  223 

precipitate  is  formed,  treating  the  rest  of  the  filtrate  as 
§117,  1,  directs.  The  residuary  precipitate  is  washed, 
dissolved  by  the  addition  of  a  few  drops  of  aqua  regia, 
ammonia  added,  till  the  solution  retains  only  a  feeble  acid 
reaction,  and  a  drop  of  it  placed  upon  a  clean  copper  plate. 
If  MERCURY  is  really  present,  a  white  stain  will  appear 
after  some  time  upon  the  copper  surface,  which  presents 
a  metallic  lustre  when  rubbed,  and  disappears  on  heating. 
Or  the  solution  in  aqua  regia  is,  with  addition  of  hydro- 
chloric acid,  evaporated  till  nearly  dry,  diluted  with  some 
water,  and  protochloride  of  tin  added.  The  formation  of 
a  precipitate,  white  at  first,  but  changing  into  gray  on  the 
protochloride  of  tin  being  added  in  excess,  is  a  safe  indica- 
tion of  the  presence  of  mercury. 

§   118. 

A  portion  of  the  fluid  in  which  solution  of  sulphuretted 
hydrogen  has  produced  no  precipitate,  (§  115,  a,)  or  of  the 
fluid  which  has  been  filtered  off  from  the  precipitate  form- 
ed, is  mixed  with  ammonia,  till  an  alkaline  reaction  be- 
comes manifest,  and  hydrosulphuret  of  ammonia  is  then 
added. 

In  cases  where  but  a  minute  quantity  of  hydrochloric 
acid  is  present,  and  where,  therefore,  but  little  muriate  of 
ammonia  has  been  formed,  a  not  too  inconsiderable  meas- 
ure of  a  solution  of  this  latter  salt  must  be  added,  previous 
to  the  addition  of  the  hydrosulphuret  of  ammonia. 

a.  No   PRECIPITATE  is  FORMED.     Pass    over  to  § 
119,  for  neither  iron,  manganese,  cobalt,  zinc,  nickel, 
oxide  of  chromium,  nor  alumina,  are  present  ;  neither 
are  the  phosphates  of  the  alkaline  earths,  nor  oxalate 
of  lime  (barytes,  strontian). 

b.  A  PRECIPITATE  is  FORMED.     The  whole  fluid  is 
treated  in  the  same  manner  as  the  first  portion. 

1.  The  precipitate  is  white.  Absence  of  iron,  cobalt,  nick- 
el. We  must  look  for  the  presence  of  all  the  other  metals 
and  compounds  enumerated  at  §  118,  a,  since  the  faint 
tints  of  sulphuret  of  manganese  and  oxide  of  chromium 
vanish  altogether  if  the  quantity  of  white  precipitate  is  con- 
siderable. The  precipitate  is  filtered  off — (the  filtrate  is- 


224  DETECTION    OF    THE  BASES. 

treated  according  to  §  119) — washed,  dissolved  in  hydro- 
chloric acid,*  boiled  up,  the  solution  filtered,  and  potash  in 
excess  added. 

a.  THE  PRECIPITATE  FORMED  AT  FIRST  ON  THE  AD- 
DITION OF  POTASH,  REDISSOLVES  COMPLETELY  IN  THE 
EXCESS  OF  THE  PRECIPITANT.  Absence  of  the  pllOS- 

phates  and  oxalates  of  the  alkaline  earths,  and  manga- 
nese. The  solution  with  potash  is  divided  into  two 
portions  ;  one  portion  is  slightly  acidified  with  hydro- 
chloric acid,  ammonia  in  excess  added,  and  the  fluid 
boiled  for  a  short  time. 

«.  No  lasting  precipitate  is  formed.  Absence  of 
.alumina  and  of  oxide  of  chromium.  Solution  of 
sulphuretted  hydrogen  is  added  to  the  other  portion 
of  the  solution  with  potash.  The  formation  of  a 
white  precipitate  indicates  ZINC. 

/3.  A  lasting  precipitate  is  formed.  It  is  filtered 
off,  and,  (should  a  green  tint  of  the  solution  with 
potash,  or  a  green,  yellow,  or  red  tint  of  the  origi- 
nal solution  make  us  conclude  that  OXIDE  OF  CHRO- 
MIUM is  present,)  a  small  portion  of  it  tested  for 
this  substance,  with  phosphate  of  soda  and  ammo- 
nia, (§  87,  b,  5,)t  solution  of  sulphuretted  hydrogen 
is  added  to  the  filtrate.  The  formation  of  a  white 
precipitate  indicates  ZINC.  For  alumina  we  test  as 
follows. 

aa.  No  oxide  of  chromium  has  been  detected. 
This  is  sufficient  to  prove  the  presence  of  ALUMI- 
NA. To  assure  ourselves  of  it  we  lest  the  precipi- 
tate produced  by  ammonia,  before  the  blow-pipe. 
(Vide  §  87,  «,  4.) 

bb.  Oxide   of  chromium   has  been  detected. 


*  If  the  precipitate  is  inconsiderable,  this  may  best  be  done  by  forcing 
it  to  the  lower  part  of  the  filter,  by  means  of  a  syringe  bottle,  allowing  the 
water  to  run  off,  and  adding  hydrochloric  acid  drop  by  drop.  If  sulphu. 
ret  of  zinc  is  present,  the  solution  effected  by  hydrochloric  acid  is  but  in. 
complete  ;  some  nitric  acid  is  added  in  that  case,  and  heat  applied. 

t  For  even  if  chromic  acid  is  present,  a  precipitate  of  oxide  of  chromi. 
•-.m  is  produced  by  hydrosulphuret  of  ammonia,  the  chromic  acid  being  re- 
duced by  sulphuretted  hydrogen.  In  such  cases,  the  yellow  or  red  colour 
'f  the  solution  changes  into  a  green  tint,  on  the  addition  of  the  sulphuret. 
)d  hydrogen J  and  sulphur  separates  at  the  same  time. 


DETECTION    OF    THE    BASES.  225 

In  this  case,  the  second  portion  of  the  solution 
with  potash  is  boiled,  until  the  oxide  of  chro- 
mium has  completely  precipitated  ;  the  fluid  is 
then  slightly  diluted,  filtered  off  from  the  oxide 
of  chromium,  slightly  acidified  with  hydrochloric 
acid,  arid  ammonia  in  excess  added.  The  forma- 
tion of  a  precipitate  indicates  ALUMINA.  The 
blow-pipe,  as  in  aa,  is  resorted  to  as  a  conclusive 
test.  Should  the  separation  of  the  oxide  of 
chromium  from  the  solution  with  potash  not 
succeed  by  boiling,  as  may  be  the  case  under 
certain  circumstances,  the  precipitate  produced 
by  ammonia  must  be  fused  with  nitre  and  car- 
bonate of  soda,  to  remove  the  chromium. 
(Vide  §  87,  6,  4.)  *'  Alumina  may  have  been 
present  as  a  PHOSPHATE,  and  may  have  precipi- 
tated as  such.  For  the  way  in  which  this  may 
be  ascertained,  we  refer  to  §  110,  1." 

b.  A.  PRECIPITATE  INSOLUBLE  IN  POTASH  HAS  RE- 
MAINED. The  solution  is  filtered  off  and  the  filtrate 
treated  as  §  118,  1,  «,  directs.  The  residuary  preci- 
pitate may  consist  of  MANGANESE,  "  of  the  phosphates 
and  oxalates  of  the  alkaline  earths."  The  presence 
of  MANGANESE  is  indicated  by  the  precipitate  assum- 
ing a  brown  colour  when  exposed  to  the  air.  The 
test  with  carbonate  of  soda  before  the  blow-pipe  is 
resorted  to  as  a  conclusive  proof.  (§  88,  6,  5.)  If 
manganese  is  present,  the  precipitate  is  dissolved  in 
hydrochloric  acid,  some  tartaric  acid  mixed  with  it, 
and  then  ammonia  in  excess  added.  If  no  precipi- 
tate is  formed,  neither  phosphates  nor  oxalates  of  the 
alkaline  earths  are  present ;  the  formation  of  a  preci~ 
pitate  indicates  the  presence  of  these  compounds. 
This  precipitate,  (or,  if  no  manganese  was  present, 
the  residuary  precipitate  undissolved  by  potash),  is 
washed  and  subjected  to  the  following  preliminary 
examination,  in  order  to  ascertain,  whether  it  consists 
of  phosphates  of  the  alkaline  earths  alone  or  of  oxa- 
lates of  the  alkaline  earths  alone,  or  whether  it  is  a 
mixture  of  both.  A  small  portion  of  the  precipitate 
is  gently  heated  upon  a  platinum  plate,  and  the  resi- 
due treated  with  hydrochloric  acid. 


226  DETECTION    OF    THE    BASES. 

*.  It  dissolves  without  effervescence :  absence 
of  oxalates.  The  rest  of  the  precipitate  is  then 
dissolved  in  hydrochloric  acid,  perchloride  of  iron 
added  in  excess,  and  then  ammonia,  and  the  fur- 
ther operations,  for  the  detection  of  the  bases  and 
of  the  phosphoric  acid,  conducted  as  directed 
§  110,  2,  a. 

/3.  It  dissolves  with  effervescence  :  presence  of 
an  oxalate.  In  this  case  a  preliminary  examina- 
tion for  phosphates  becomes  necessary.  For  this 
purpose  the  hydrochloric  solution  is  boiled,  to 
expel  the  carbonic  acid,  and  ammonia  added. 

aa.  No  precipitate  is  formed.  Absence  of 
phosphates :  oxalates  alone  can  be  present. 
For  the  detection  of  the  bases,  and  the  confirma- 
tory examination  for  oxalic  acid,  vide  §  110, 
2,  b. 

bb.  A  precipitate  is  formed:  presence  of  a 
phosphate  and  an  oxalate.  The  rest  of  the  pre- 
cipitate is  then  heated  to  redness  and  dissolved 
in  very  slightly  diluted  hydrochloric  acid ;  the 
solution  is  boiled  to  expel  the  carbonic  acid  ; 
ammonia  in  excess  is  added,  and  the  solution  fil- 
tered. The  earths  which  were  combined  with 
the  oxalic  acid,  are  detected  in  the  filtrate,  as 
§  119  directs.  The  precipitate  is  treated  as 
stated  §  118,  1,  b. 

2.    THE  PRECIPITATE  PRODUCED    BY    HYDROSULPHURET  OF 

AMMONIA  is  NOT  WHITE  ;  this  indicates  chromium,  manga- 
nese, iron,  cobalt,  or  nickel.  If  the  precipitate  is  black 
or  has  a  shade  of  black,  one  of  the  three  latter  metals  is 
certainly  present.  But,  under  all  circumstances,  we  must 
look  for  all  the  metals  and  compounds  enumerated  §  1 18,  a. 
The  precipitate  is  filtered  off  from  the  solution— (the  fil- 
trate is  treated  as  §  119  directs) — carefully  washed  and 
treated  with  dilute  hydrochloric  acid. 

a.  No  SOLUTION  TAKES  PLACE,  OR  THE  SOLUTION  IS  IN- 
COMPLETE INASMUCH  AS  THE  BLACK  COLOUR  OF  THE  PRECI- 
PITATE DOES  NOT  'DISAPPEAR  J  COBALT,  NICKEL-  Some 

nitric  acid  is  then  added  to  the  hydrochloric  acid,  and  the 
solution  boiled  and  treated  as  follows.  The  fluid  is  filtered 


DETECTION  OF  THE  BASES.  227 

off  from  the  separated  sulphur,  and  a  small  portion  of  it 
mixed  with  solution  of  sal  ammoniac,  ammonia  in  excess 
added,  and  heat  applied. 

a.      No    LASTING    PRECIPITATE     IS     FORMED     BY 

AMMONIA  :  absence  of  peroxide  of  iron,  oxide  of 
chromium,  alumina,  phosphates  and  oxalates  of  the 
alkaline  earths.  The  rest  of  the  acid  solution  of 
the  sulphurets  is  mixed  with  caustic  potash  in 
excess,  heated,  and  the  fluid  filtered  off  from  the 
precipitate  formed.  The  filtrate  is  tested  for  zinc 
with  solution  of  sulphuretted  hydrogen.  (Compare 
§  118,  1,  a,  *.)  The  precipitate  is  washed  and 
drenched,  heated  and  agitated  for  some  time  with 
a  somewhat  considerable  quantity  of  solution  of 
carbonate  of  ammonia,  mixed  with  half  its  measure 
of  caustic  ammonia. 

aa.  The  precipitate  is  completely  redissolved. 
Absence  of  manganese.  The  ammoniacal  solu- 
tion is  evaporated  to  dryness,  the  residue  dis- 
solved in  a  few  drops  of  hydrochloric  acid,  once 
more  slightly  evaporated,  and  a  portion  of  a  resi- 
due— (which  should  still  be  moist)  — tested  for 
COBALT,  with  borax,  (§  88,  d,  7.)  The  rest  of 
the  moist  residue  is  then  dissolved  in  some 
.  water,  and  solution  of  cyanide  of  potassium 
added,  till  the  precipitate  formed  at  first,  is  re- 
dissolved  in  an  excess  of  cyanide  of  potassium  ; 
dilute  sulphuric  acid  is  then  added  and  heat 
applied ;  the  solution  is  allowed  to  stand  for 
some  time.  The  formation  of  a  greenish  white 
precipitate,  immediately  or  after  the  lapse  of 
some  time,  indicates  NICKEL.  (§  88,  c.  6,  and 
Recapitulation  and  Remarks,  §  88.) 

bb.  An  insoluble  residue  remains,  on  treating 
the  precipitate  produced  by  caustic  potasht  with 
carbonate  of  ammonia  and  caustic  ammonia. 
This  is  tested  for  MANGANESE,  with  carbonate  of 
soda.  (§  88,  bj  5.)  If  the  precipitate  really 
consists  of  protoxide  of  manganese,  it  may  almost 
always  safely  be  detected  by  its  assuming  a 
brown  tint,  when  exposed  to  the  air.  The  am- 


228  DETECTION    OF    THE    BASES. 

moniacal  solution  is  tested  for  cobalt  and  nickel, 

as  directed  §  1 18,  2,  a,  <*,  aa.    • 

ft.  AMMONIA  PRODUCES  A  LASTING  PRECIPITATE. 
The  entire  solution  of  the  sulphurets  in  aqua  regia 
is  then  treated  in  the  same  manner  as  the  first  por- 
tion, the  precipitate  produced  by  ammonia,  in  pre- 
sence of  sal  ammoniac,  is  filtered  off  from  the 
solution  and  washed ;  the  further  operations  for 
testing  both  the  filtrate  and  precipitate  are  con- 
ducted as  follow. 

1.  Hydrosulphuret  of  ammonia  is  added  to  the  FILTRATE, 
till  it  causes  no  longer  any  precipitation  ;  the  precipitate 
obtained  is  filtered  off  from  thesolution,  carefully  was  hed, 
dissolved  in  aqua  regia,   mixed  with  caustic  potash  in 
excess  and  tested  for  cobalt,  nickel,  manganese,  and  zinc, 
exactly  as  $  118,  2,  a,  *,  directs. 

2.  The  PRECIPITATE  is  digested  with  dilute  solution  of 
potash.     (If  we  have  obtained  only  a  very  minute  precipi- 
tate, this   should  be  dissolved,  on  the  filter,  by  means  of 
hydrochloric  acid,  and  caustic  potash  in  excess  added  to 
tne  solution.) 

aa.  The  precipitate  redissolves  completely  in. 
the  caustic  potash  :  absence  of  peroxide  of  iron, 
and  of  the  phosphates,  and  oxalates  of  the  alka- 
line earths.  The  solution  with  potash  is  tested 
for  alumina  and  oxide  of  chromium,  exactly  as 
§  118,  1,0,  directs. 

bb.  The  precipitate  does  not  redissolve,  or  at 
least  not  completely.  The  solution  is  filtered 
and  the  filtrate  tested  for  oxide  of  chromium  and 
alumina,  as  stated  at  aa.  The  residue  is  dis- 
solved in  dilute  hydrochloric  acid,  and  a  small 
portion  of  the  solution  mixed  with  ferrocyanide 
of  potassium.  The  immediate  formation  of  a 
•  blue  precipitate  or  even  a  blue  tint  in  the  solu- 
tion indicates  IRON.  If  iron  is  present,  the  rest 
of  the  hydrochloric  solution  is  mixed  with  some 
tartaric  acid,  and  ammonia  in  excess  added. 
Should  no  iron  be  present,  the  solution  is  simply 
supersaturated  with  ammonia.  If  no  precipitate 
is  formed,  neither  phosphates  nor  oxalates  of  the 


DETECTION    OF    THE    BASES.  229 

alkaline  earths  are  present ;  if  a  precipitate  is 
formed,  this  is  treated  as  §  118,  1,  6,  directs. 
To  ascertain  whether  the  iron  was  present  as 
peroxide  or  protoxide,  the  original  solution  in 
water  or  in  hydrochloric  acid  (but  not  in  nitric 
acid)  is  tested  with  ferrocyanide  of  potassium 
and  with  ferricyanide  of  potassium.  The  forma- 
tion of  a  dark  blue  precipitate  with  the  former 
reagent,  indicates  PEROXIDE  j  with  the  latter, 
PROTOXIDE, 
b.  THE  PRECIPITATE  PRODUCED  BY  HYDROSULPHURET 

OF  AMMONIA  REDISSOLVES  READILY  AND  COMPLETELY 
UPON  BEING  TREATED  WITH  HYDROCHLORIC  ACID,  OR, 
AT  LEAST,  ITS  BLACK  COLOUR  DISAPPEARS  IMMEDIATELY  : 

absence  of  cobalt  and  nickel.  The  solution  is  boiled 
with  some  nitric  acid,  filtered  off  from  the  sulphur 
which  precipitates  in  this  operation,  and  a  small  por- 
tion of  the  filtrate  mixed  with  sal  ammoniac  J  ammonia 
in  excess  is  then  added  and  heat  applied. 

•  a..  No  lasting  precipitate  is  formed  upon  the  ad- 
dition of  ammonia:  absence  of  iron,  oxide  of  chro- 
mium, alumina  phosphates,  and  oxalates  of  the  alka- 
line earths.  The  rest  of  the  hydrochloric  solution  is 
mixed  with  potash  in  excess,  and  the  precipitate 
formed  tested  for  MANGANESE,  with  carbonate  of 
soda ;  the  alkaline  filtrate  is  tested  for  ZINC,  with 
sulphuretted  hydrogen. 

£.  A  lasting  precipitate  is  formed  upon  the  ad- 
dition  of  ammonia*  The  entire  solution  of  the 
sulphurets  is  treated  in  the  same  manner  as  the 
first  portion.  The  precipitate  is  tested  exactly  as 
§  118,  2,  a,  /3,  2  directs.  The  solution  which  has 
been  filtered  off  from  the  precipitate,  is  mixed 
with  hydrosulphuret  of  ammonia  in  excess. 

aa.  No  precipitate  is  formed :  absence  of 
manganese  and  zinc, 

bb.  A  precipitate  is  formed.  This  is  well 
washed  and  dissolved  in  aqua  regia,  and  potash 
in  excess  added  to  the  solution. 

<*«.  No  lasting  precipitate  is  formed:  ab- 
sence of  manganese  and  consequently  prej 
10 


230  DETECTION    OF  THE   BASES. 

gence  of  ZINC,  For  further  proof  sulphuretted 
hydrogen  is  added  to  the  solution  with  potash, 
p/3.  A  precipitate  is  formed :  MANGANESE* 
The  blow-pipe  is  resorted  to  as  a  conclusive 
te&t.  The  fluid  which  has  been  filtered  off 
from  this  precipitate  is  treated  with  sulphu- 
retted hydrogen.  The  formation  of  a  white 
precipitate  indicates  ZINC. 

§  119. 

A  portion  of  the  fluid  in  which  hydrosulphuret  of  am- 
monia has  produced  no  precipitate,  or  which  has  been  fil- 
tered off  from  the  precipitate  formed,  is  mixed  with  phos- 
phate of  soda  and  with  ammonia — (if  it  does  not  already 
contain  free  ammonia) — and  strongly  agitated. 

a.  No  PRECIPITATE  is  FORMED  j  this  indicates  the 
absence  of  all  the  alkaline  earths.     A  fresh  portion  of 
the  fluid  is  evaporated  to  dryness  and  the   residue 
heated  to  redness.  If  no  residue  remains,  (on  heating 
to  redness,)  neither  potash  nor  soda  are  present :  pass 
over  to  §  122.«   If  a  residue  remains,  the  entire  fluid 
is  treated  in  the  same  manner  as  the  first  portion, 
and  the  further  operations  are  conducted  as  §    121 
directs. 

b.  A  PRECIPITATE*  is  FORMED.    The  remainder  of 
the  fluid,  if  containing  sulphuretted  hydrogen  or  hy- 
drosulphuret  of  ammonia — (in  which  latter  case  it 
must  first  be   acidified  with  hydrochloric  acid) — is 
heated,  till  it  has  lost  all  odour  of  sulphuretted  hydro- 
gen, and  then  filtered  off  from  the  sulphur,  if  any  has 
been  precipitated.    To  this  filtrate  a  mixture  of  car- 
bonate  of  ammonia   and  some  caustic  ammonia  is 
added  in  excess — after  having  previously  added  mu- 
riate of  ammonia,  should  this   substance  not  already 
have  been  formed  in  the  fluid  in  sufficient  quantity 
during  the  course  of  examination.     The  solution  is 
boiled  for  some  time. 

1.  No  PRECIPITATE    IS    FORMED.     PaSS    OVCr  tO    §    120, 

neither  lime,  nor  barytes,  nor  strontian  being  present. 

2.  A   PRECIPITATE    IS   FORMED!   presence  of    LIME,  BA- 

w. 


DETECTION    OF    THE   BASES.  231 

RYTES,  or  STRONTIAN.     The  precipitate  is  filtered  off — 

(the  filtrate  is  tested  as  §  120  directs) — and  dissolved  in 

the  least  possible  quantity  of  very  dilute  hydrochloric  acid. 

a.  Solution  of  gypsum  is  added  to  a  portion  of  the 

solution. 

*.  No  precipitate  is  formed,  NOT  EVEN  AFTER 

THE    LAPSE   OF   SOME   TIME.       PaSS  OVCr  tO  §  119,  2, 

b}  for  barytes  and  strontian  are  not  present- 
/3.  A  precipitate  is  formed. 

aa.  It  is  formed  Immediately  upon  the  addition 
of  the  soluution  of  gypsum  :  this  indicates  BARY- 
TES. Strontian  may  be  present  besides. 

A  portion  of  the  hydrochloric  solution  (vide  § 
119,  2)  is  evaporated  to  dry  ness,  and  the  residue 
digested  with  absolute  alcohol — (at  least,  with 
very  strong  alcohol)  — and  the  solution  filtered. 
A  few  drops  of  the  filtrate  are  evaporated  upon 
a  platinum  plate. 

*«.  No  residue  remains.  Passover  to  §  120: 
for  neither  strontian  nor  lime  are  present. 

/3/3.  A  residue  remains.  The  alcoholic  so- 
lution is  divided  into  two  portions :  one  portion 
is  heated  in  a  small  crucible  and  ignited ;  a 
carmine  red  tint  of  the  flame  indicates  STRON- 
TIAN. If  the  flame  does  not  appear  red,  or  if 
any  doubt  exists  as  to  its  exact  tint,  the  second 
portion  of  the  alcoholic  solution  is  evaporated 
to  dryness,  the  residue  dissolved  in  a  small 
proportion  of  water,  and  the  solution  tested 
with  solution  of  gypsum.  The  formation  of  a 
precipitate  after  the  lapse  of  some  time,  indi- 
cates STRONTIAN. 

We  can  best  assure  ourselves  of  the  pre- 
sence of  barytes  by  adding  hydrofluosilicic 
acid  to  the  solution  in  hydrochloric  acid,  and 
applying  heat.  The  formation  of  a  precipitate 
after  the  lapse  of  some  time  denotes  the  pre- 
sence of  BARYTES. 

bb.  The  precipitate  is  formed,  only  after  the 
lapse  of  some  time :  absence  of  barytes  ;  pre- 
sence of  STRONTIAN. 


232  DETECTION  OF   THE    BASES. 

b.  Oxalic  acid  is  added  to  a  fresh  portion  of  the 
hydrochloric  solution,  (vide  §  119,  2,)  after  having 
previously  made  it  alkaline  by  the  addition  of  ammonia. 
Should  (after  §  1 19,  2,  a,  /3,)  barytes  or  strontian  have 
been  detected,  these  must  be  first  precipitated  with 
sulphate  of  potash,  the  solution  filtered  off,  and  the 
oxalic  acid  added  to  the  filtrate,  after  the  previous  ad- 
dition of  ammonia.  If  a  precipitate  is  formed,  lime 
is  present. 

§  120. 

Two  small  portions  are  taken  of  the  fluid,  in  which  car- 
bonate of  ammonia  has  produced  no  precipitate,  (§119,  1.) 
or  of  that  which  has  been  filtered  off  from  the  precipitate 
formed,  and  sulphate  of  potash  is  added  to  the  one,  oxalate 
of  ammonia  to  the  other. 

1.  BOTH  THESE  REAGENTS  PRODUCE  NO  LONGER  ANY 

PRECIPITATE.  This  is  a  certain  proof  that  all  barytes, 
strontian,  and  lime,  have  been  completely  precipitated  by 
carbonate  of  ammonia.  Phosphate  of  soda  is  added  to  a 
third  portion  of  the  fluid  with  carbonate  of  ammonia,  and 
the  mixture  stirred  with  a  glass  rod.  The  formation  of  a 
crystalline  precipitate,  (vide  §  86,  d,  5,)  indicates  MAGNE- 
SIA. The  rest  of  the  fluid,  a  portion  of  which  has  been 
tested  for  magnesia,  is  evaporated  to  dryness,  and  heated 
till  all  the  ammoniacal  salts  have  been  expelled.  If  no  re- 
sidue remains,  pass  over  to  §  122;  if  a  residue  remains, 
pass  over§  121. 

2.  BOTH  THE  REAGENTS,  OR  AT  LEAST  ONE  OF  THEM, 

PRODUCE  STILL  A  PRECIPITATE.  In  that  case,  barytes, 
strontian,  and  lime,  have  not  yet  been  completely  precipi- 
tated by  carbonate  of  ammonia.  This  reagent,  mixed 
with  caustic  ammonia,  is,  therefore,  once  more  added  to 
the  rest  of  the  fluid,  and  the  mixture  again  boiled  for  some 
time.  The  precipitate  formed  is  filtered  off  from  the  fluid, 
and  again  treated  as  §  120  directs. 

§  121. 

We  have  now  still  to  treat  of  the  examination  for  fixed 
alkalies  and  for  ammonia. 


DETECTION  OP  THE  BASES.  233 

The  combinations  of  the  former  are,  with  very  few  ex- 
ceptions, soluble  in  water.  It  is,  therefore,  not  necessary 
to  look  for  them  when  testing  compounds  insoluble  in 
water. 

When  we  have  to  operate  upon  a  substance  insoluble 
in  water,  but  soluble  in  hydrochloric  acid,  or  in  nitric  acid, 
a  portion  of  the  fluid,  in  the  specimen  of  which  phosphate 
of  soda  did  produce  no  precipitate,  (§  119,  a,) — or  of  that 
in  which  carbonate  of  ammonia  has  occasioned  none, 
(§  119,  1,)  or  of  that  which  has  been  filtered  off  from  the 
precipitate  formed,  (§  119,  23) — is  preserved  and  tested  for 
phosphoric  acid  and  oxalic  acid,  as  §  1 25,  8,  directs. 

1.  MAGNESIA  is  NOT  PRESENT.     The  roasted  residue 
of  §119,  «,  is  dissolved  in  a  small  proportion  of  water, 
and  alcohol  added  to  the  solution  ;  this  is  then  heated  to 
the  boiling  point  and  ignited. 

a.  THE  FLAME  HAS  A  VIOLET  TINT.     Absence  of 
soda  ;  probable  presence  of  POTASH. 

b.  THE  FLAME  is  YELLOW  :  presence  of  SODA.  The 
solution  is  evaporated  to  dryness,   and  the  test  with 
antimoniate  of  potash,  and  the  blow-pipe  flame,  are 
resorted  to  as  conclusive  proofs  of  the  presence  of 
soda.  (Vide  $  85,  6,  3.)     We  assure  ourselves  of  the 
presence  of  potash,  by  dissolving  this  residue  in  wa- 
ter, or,  better  still,  in  alcohol,  if  possible,  and  heating 
one  half  of  the  solution  with  tartaric  acid,  and  the 
other  half  with  chloride  of  platinum.     If  potash  be 
present,  the  tartaric  acid  will  produce  a  colourless, 
granular,  crystalline  precipitate,   after  the   lapse  of 
some  time,  whilst  the  chloride  of  platinum  will  pro- 
duce a  yellow  precipitate. 

2.  MAGNESIA  is  PRESENT.     The  residue  is  dissolved  in 
water,   and  water  of  barytes,  or  solution  of  sulphuret  of 
barium  (containing  caustic  barytes)  added,  as  long  as  any 
precipitate  is  formed ;  the  solution  is  then  boiled,  filtered, 
and  dilute  sulphuric  acid  dropped  into  the  filtrate  till  the 
reaction  has  become  acid.     The  fluid  is  then  filtered  off 
from  the  precipitated  sulphate  of  barytes,  the  filtrate  eva- 
porated to  dryness,  and  the  residue  which,  perchance,  may 
remain,  tested  for  potash  and  soda,  as  directed  §  121,  1. 
Or  the  residue  containing  magnesia  (and  perhaps  alkalies 


234  ABSENCE  OF  ORGANIC   ACIDS. 

besides)  is  treated  with  sulphuric  acid,  the  solution  evapo- 
rated to  dryness,  and  the  residue  heated  to  redness  as  long 
as  any  vapour  escapes  ;  the  residuary  mass  is  then  dis- 
solved in  water,  and  the  solution  precipitated  by  acetate  of 
barytes  in  excess,  filtered  off  from  the  precipitate,  and  the 
filtrate  again  evaporated  to  dryness  ;  the  residue  is  exposed 
to  a  strong  red  heat,  and  then  treated  with  a  small  propor- 
tion of  water ;  the  solution  is  filtered  and  further  tested  for 
potash  and  soda,  as  §  121,  1,  directs.  Should  the  filtrate 
manifest  an  alkaline  reaction,  it  must  first  be  neutralized 
with  hydrochloric  acid. 

§122. 

We  have  now  still  to  consider  the  examination  for  am- 
monia. A  portion  of  the  substance  under  examination  is 
treated  with  concentrated  solution  of  potash,  and  heat 
applied.  AMMONIA  is  present,  if  the  escaping  gas  emits 
its  characteristic  odour,  if  it  restores  the  blue  colour  of 
moist  reddened  litmus-paper,  and  if  white  fumes  arise  upon 
a  small  glass  rod,  moistened  with  hydrochloric  acid,  being 
dipped  into  the  tube. 

Compounds  in  which  all  the  more  frequently  occurring 
acids  and  bases,  metals  and  metalloids,  are  supposed  to 
be  present. 

A.  1.  SUBSTANCES  SOLFBLE  IN  WATER.  DETECTION  OF  ACIDS 

AND  METALLOIDS. 

I.  Absence  of  Organic  Acids. 
§  123. 

1.  Concerning  the  detection  of  ARSENIOUS  and  ARSENIC 

ACID,  CARBONIC  ACID,  HYDROSULPHURIC  ACID,  and  CHROMIC 

ACID,  compare  §  108,  1  and  2. 

2.  Nitrate  of  barytes  is  added  to  a  portion  of  the  solu- 
tion ;  if  the  solution  is  acid,  it  must  first  be  neutralized 
with  ammonia. 

a.  No  PRECIPITATE  is  FORMED.     Absence  of  sul- 
phuric  acid,  phosphoric  acid,  boracic  acid,  chromic 


ABSENCE    OF  ORGANIC  ACIDS.  235 

acid,  silicic  acid,  oxalic  acid,  arsenious  and  arsenic 
acid.*     (Pass  over  to  &) 

b.  A.  PRECIPITATE  is  FORMED.  The  fluid  is  di- 
luted,  and  hydrochloric  acid  added  ;  if  the  precipitate 
does  not  redissolve,  or,  at  least,  not  completely,  SUL- 
PHURIC ACID  is  present. 

S.  Nitrate  of  silver  is  added  to  a  portion  of  the  solution ; 
Shis  is  previously  EXACTLY  neutralized,  if  acid,  by  means 
©f  ammonia  ;  if  alkaline,  by  means  of  nitric  ac^d, 

a.  No  PRECIPITATE  is  FORMED.     Pass  over  to  4 ; 
neither    chlorine,   nor  iodine,   cyanogen,  phosphoric 
acid,  silicic  acid,  oxalic  acid,  nor  chromic  acid  are 
present,  nor  boracic  acid,  if  the  solution  was  not  too 
dilute- 

b.  A  PRECIPITATE  is  FORMED.     The  colour  of  the 
precipitate   is  inspected,    and  the   nitric  acid  then 
added. 

«.  The  precipitate  redissolves  completely.    Pass 

over  to  §  1 23,  4 ;  for  neither  chlorine,  iodine,  nor 

cyanogen  are  present. 

/s.  A  residue  remains:    CHLORINE,  IODINE,  or 

CYANOGEN.     The  residue  is  washed  and  digested 

with  ammonia. 

aa.  A  yellowish  residue  remains.  This  is 
caused  by  the  presence  of  IODINE.  We  assure 
ourselves  of  the  presence  ©f  this  substance  as 
§  100,  c,  directs.  The  solution  is  filtered  off 
from  the  residue,  and  nitric  acid  in  excess  added 
to  the  filtrate ;  if  a  precipitate  is  formed,  it  indi- 
cates chlorine  or  cyanogen.  For  the  further 
operation,  vide  bb* 

bb.  No  residue  remains^  CHLORINE  or  CYANO- 
GEN ;  absence  of  iodine.  For  further  examina- 
tion, the  solution  is  again  precipitated  with  nitric 
acid.  Previous  to  beginning  the  operation  of 
distinguishing  chloride  of  silver  from  cyanide  of 

*  If  muriate  of  ammonia  is  present  in  the  fluid  under  examination,  the 
non-formation  of  a  precipitate  is  not  a  conclusive  proof  of  the  absence  of 
oxalic  acid,  arsenious  and  arsenic  acid,  and  especially  not  of  that 'of  bo- 
racic acid,  the  barytes  salts  of  these  acids  not  being  insoluble  in  water,  in 
presence  cf  anamoni&cal  salts. 


236  ABSENCE  OF  ORGANIC  ACIDS. 

silver,  the  fluid  is  tested  for  cyanogen,  in  order 
to  see  whether  this  operation  is  at  all  necessary. 
For  this  purpose  solution  of  magnetic  oxide  of 
iron  is  added  to  a  portion  of  the  original  solu- 
tion, followed  by  the  addition  of  hydrochloric 
acid.  The  formation  of  a  blue  precipitate  indi- 
cates CYANOGEN.*  If  no  precipitate  is  formed, 
and  the  fluid  assumes  no  blue  tint,  the  precipitate 
redissolved  by  ammonia  consists  of  chloride  of 
silver  alone.  If  cyanogen  has  been  detected,  the 
precipitate  to  be  examined  is  washed,  taken  from 
the  filter  when  still  mcist,  dried  in  a  porcelain 
crucible,  and  heated  to  redness.  Chloride  of 
silver  merely  fuses,  whilst  cyanide  of  silver  be- 
comes reduced.  The  metallic  silver  may  be 
separated  from  the  chloride  of  silver  by  means 
of  nitric  acid. 

4.  The  aqueous  solution  is  tested  for  nitric  acid,   by 
mixing  solution  of  indigo  with  it,  till  it  has  acquired  a  light 
blue  tint,  and  then  adding  some  sulphuric  acid,  and  apply- 
ing heat ;  and,  moreover,  by  throwing  a  crystal  of  proto- 
sulphate  of  iron  into  the  solution,  previously  mixed  with 
the  third  part  of  its  amount  of  concentrated  sulphuric  acid. 
If  nitric  acid  is  present,  the  blue  solution  loses  its  colour, 
and  a  brown-coloured  halo  forms  round  the  crystal. 

We  have  now  still  to  speak  of  the  examinations  for  phos- 
phoric acid,  boracic  acid,  silicic  acid,  oxalic  acid,  and  chro- 
mic acid.  It  is  necessary  to  make  these  examinations  only 
in  such  cases  where  chloride  of  barium,  as  well  as  nitrate  of 
silver,  have  caused  the  formation  of  precipitates,  in  neutral 
solutions.  Compare  note  to  §  123,  2,  a. 

5.  If  the  precipitate  produced  by  nitrate  of  silver  was  of 
a  yellowish  colour,  we  must  especially  look  for  phosphoric 
acid.     For  this  purpose,  ammonia  in  excess  is  added  to  a 
portion  of  the  fluid ;  if  a  precipitate  is  formed,  the  fluid  is 
filtered,  and  muriate  of  ammonia  added  to  the  filtrate,  and 

*  Should  the  cyanogen  be  present  as  free  hydrocyanic  acid,  which  may 
easily  be  detected  by  its  characteristic  odour,  this  ought  to  be  saturated 
with  potash,  previous  to  the  addition  of  the  solution  of  iron.  We  have 
already  stated  at  §  100,  d,  that  the  cyanogen  is  not  detected  by  nitrate  of 
silver,  in  certain  combinations,  e.  g.  cyanide  of  mercury. 


ABSENCE    OF    ORGANIC   ACIDS.  237 

then  sulphate  of  magnesia.    The  formation  of  a  crystalline 
precipitate  denotes  PHOSPHORIC  ACID- 

6.  A  small  portion  of  the  substance  under  examination  is 
drenched  with  alcohol,  sulphuric  acid  added,  and  the  mixture 
heated  to  boiling  in  a  small  crucible,  and  then  ignited.     If 
the  flame  has  a  green  tint,   BORACIC  ACID  is  present.     If 
copper  is  present,  this  must  first  be  removed,  either  by 
means  of  sulphuretted  hydrogen,  or  by  boiling  the  fluid  with 
potash  in  excess. 

7.  If  the  fluid  was  red,  or  yellow  changing  to  red,  on  the 
addition  of  hydrochloric  acid,  and  if  the  precipitate  produ- 
ced by  nitrate  of  silver  in  the  neutral  solution  had  a  purple 
red  colour,  the  presence  of  CHROMIC  ACID  is  confirmed. 

8.  For  silicic  acid,  test  as  §  99,  b,  2,  directs. 

9.  For  the  detection  of  OXALIC  ACID,  solution  of  gypsum 
is  added  to  a  portion  of  the  fluid  under  examination,  which 
must  first  be  neutralized  with  ammonia,  if  it  manifests  an 
acid  reaction.     The  formation  of  a  white  precipitate,  which 
does  not  vanish  upon  the  addition  of  acetic  acid,  indicates 
the  presence  of  oxalic  acid. 

CHLORATES,  BROMIDES,  and  FLUORIDES,  are  of  less  fre- 
quent occurrence.  Chlorates  may  be  detected  by  their 
violent  deflagration  with  charcoal,  when  in  a  state  of  fusion, 
(vide  §  105,  A.  I.  2,  c.)  Chloric  acid  is  best  detected  by 
heating  a  portion  of  the  solid  salt  in  a  glass  tube,  closed  at 
the  lower  end,  and  placing  a  wood-splinter  which  has  been 
kindled  and  the  flame  extinguished,  near  the  open  end.  If 
CHLORIC  ACID  be  present,  the  flame  of  the  wood-splinter 
will  be  rekindled.  The  residue  dissolved  in  water  yields 
in  that  case  with  nitrate  of  silver  a  copious  precipitate  of 
chloride  of  silver.  Other  tests  are,  to  throw  a  few  grains 
of  the  salt  into  fuming  sulphuric  acid,  (§  101,  b.  6,)  or  fus- 
ing a  portion  of  the  salt  with  cyanide  of  potassium.  (§  101, 
b,  3.)  The  detection  of  BROMIDES  is  simple,  if  iodides 
are  not  present,  at  the  same  time.  Vide  §  100,  for  the 
safe  detection  of  bromine  in  both  cases.  For  the  detec- 
tion of  the  FLUORIDES,  the  methods  described  §  98,  d,  4 
and  5,  are  the  safest  under  all  circumstances. 
10* 


238  PRESENCE    OF    ORGANIC    ACIDS. 


Compounds  in  which  all  the  more  frequently  occurring 
acids  and  bases,  metals  and  metalloids,  are  supposed  to 
be  present. 

A.  1.  SUBSTANCES  SOLUBLE  IN  WATER.     DETECTION  OF 

ACIDS    AND    METALLOIDS. 

II.     Presence  of  Organic  Acids. 
§  124. 

1.  CHROMIC  ACID,  ARSENIOUS,  and  ARSENIC  ACID,  have 
already  been  detected  when  testing  for  the  bases  ;  concern- 
ing the  distinction  of  arsenious  from  arsenic  acid,  compare 
§  93,  additions  and  remarks. 

2.  Hydrochloric  acid  is  added  to  a  portion  of  the  solu- 
tion.    The  formation  of  a  precipitate,  which,  upon  being 
heated  on  a  platinum  plate  volatilizes  partly  or  totally, 
emitting  the  characteristic  odour  of  BENZOIC  ACID,  indicates 
the  presence  of  this  acid.     Effervescence,  upon  the  addition 
of  the  hydrochloric  acid,  may  be  caused  by  the  presence 
of  CARBONIC  ACID,  or  by  that  of  SULPHURETTED  HYDROGEN. 
(Vide  §  108,  2.) 

3.  Ammonia  is  added,  to  a  portion  of  the  solution,   till 
the  latter  manifests  a  feebly  alkaline  reaction  ;  the  solu- 
tion is  then  filtered,  if  necessary,  and  chloride   of  barium 
added. 

Should  hydrochloric  acid  have  produced  a  precipi- 
pitate  in  the  original  solution,  the  nitrate  of  this  ought 
to  be  used  for  this  experiment. 

a.  No  PRECIPITATE  is  FORMED.     Absence  of  sul- 
phuric  acid,  phosphoric  acid,   chromic   acid,  boracic 
acid,  arsenic  acid,  arsenious  acid,  silicic  acid,  oxalic 
acid,  tartaric  acid,  citric  acid ;  these  may,  therefore, 
be  disregarded  in  the  further  course  of  examination. 
What  we  have  stated  at  §  123,  2,  a,  (note,)  applies 
also  to  the  last  six  of  these  acids. 

b.  A  PRECIPITATE  is  FORMED.     Hydrochloric  acid 
is  added. 

<*.   The  precipitate  redissolves  :     Absence  of 
sufphuric  acid. 
0.  A  residue  remains  :  SULPHURIC  ACID. 


PRESENCE    OF    ORGANIC    ACIDS.  239 

4.  Nitrate  of  silver  is  added  to  a  portion  of  the  solution, 
which  must  first  be  EXACTLY  neutralized  with  nitric  acid, 
if  alkaline,  and  with  ammonia,  if  acid. 

a.  No  precipitate  is  formed  »  absence  of  phospho- 
ric acid,  boracic  acid,  chromic  acid,  silicic  acid,  oxalic 
acid,  tartaric  acid,  citric  acid ;  these  may,  therefore, 
be  disregarded  in  the  further  course  of  examination. 

b.  A  PRECIPITATE  IS  FORMED. 

<*.  It  is  whitish  or  yellow.  A  portion  of  the  fluid, 
together  with  the  precipitate  suspended  therein,  is 
boiled.  Complete  and  rapid  reduction  indicates 
FORMIC  ACID.  Protonitrate  of  mercury  is  used  as 
a  conclusive  test,  §  104,  6,  bearing  in  mind  the 
remarks  which  will  be  found  at  the  end  of  this 
number,  (4.)  The  rest  of  the  precipitate  is  treated 
with  nitric  acid.  If  it  is  redissolved,  neither  CHLO- 
RINE, nor  IODINE,  nor  CYANOGEN,  are  present ;  but 
if  the  precipitate  does  not  completely  redissolve  in 
nitric  acid,  the  residue  is  tested  for  these  salt  radi- 
cals, as  §  123,  3,  6,  /3,  directs. 

/3.  The  precipitate  produced  by  nitrate  of  silver 
is  purple  :  CHROMIC  ACID.  Should  arsenic  acid  be 
present,  acetate  of  lead  is  added,  or  (as  a  conclu- 
sive test,  to  a  fresh  portion  of  the  solution)  the 
formation  of  a  yellow  precipitate  proves  the  pre- 
sence of  CHROMIC  ACID,  CHLORINE,  IODINE,  and 

CYANOGEN,  may  also  be  present  in  the  silver  pre- 
"•     cipitate:  test  for  these  salt  radicals  as  §  123,  3,  6, 
directs. 

In  the  presence  of  chromic  acid,  formic   acid 
cannot  be  detected  with  certainty,  by  the  reduction 
of  silver  and  mercury.     In  this  case  there  remains 
no  other  means  of  its  certain  detection,  except  dis- 
tilling the  compound  under   examination,  with  the 
addition  of  some  sulphuric  acid.     The  distillate  is 
saturated  with  soda,  and  then  tested  with  perchlo- 
ride  of  iron,  (which  chromic  acid  tinges  blood-red,) 
and  with  nitrate  of  silver.     (Compare  §  104,  b,) 
5.  If  chloride  of  barium  and  nitrate  of  silver  have  given 
rise  to  the  formation  of  precipitates,  test  for  PHOSPHORIC 
ACID,  as  directed  §  123,  5,  and  for  SILICIC  ACID  as  directed 
§  99,  6,  2. 


240  PRESENCE    OF    ORGANIC    ACIDS. 

6.  A  portion  of  the  solid  substance  under  examination 
(or,  if  in  solution — (should  the  latter  be  acid,  it  must  first 
be  saturated  with  potash) — the  residue  obtained  by  eva- 
porating the  solution  to  dryness)  is  drenched  with  alcohol 
in  a  small  tube,  concentrated  sulphuric  acid  to  the  extent 
of  about  one-third  of  the  volume  of  the  alcohol,  and  the 
mixture  heated  to  the  boiling  point.     If  any  odour  of  acetic 
ether  is  emitted — which,  in  many  instances,  may  be  clearly 
detected  upon  agitating  the   mixture,  whilst   cooling  or 
when  cold — ACETIC  ACID  is  present.     The  contents  of  the 
tube  are  poured  into  a  small  crucible,  heated,  and  ignited. 
If  the  flame  is  green,  BORACIC  acid  is  present. 

7.  A  portion  of  the  fluid  is  rendered  feebly  alkaline  by 
the  addition  of  ammonia,  filtered,   if  necessary,  and  chlo- 
ride of  calcium  added.     If  the  solution  was  neutral,  some 
sal  ammoniac  must  be  added  before  the  addition  of  chlo- 
ride of  calcium. 

a.  No  PRECIPITATE   IS    FORMED,  NOT    EVEN    AFTER 

THE  LAPSE  OF  SOME  TIME.     Absence  of  oxalic  acid 
and  tartaric  acid ;  pass  over  to  8. 

b.  A    PRECIPITATE     IS    FORMED     IMMEDIATELY,    OR 
AFTER  THE  LAPSE   OF  A  FEW  MINUTES.       The  Solution 

is  filtered  off  from  this  precipitate,   and   the  filtrate 
further  tested  as  8  directs. 

The  precipitate  is  washed,  digested,  and  agitated 
with  somewhat  dilute  solution  of  potash  in  excess, 
without  the  aid  of  heat,  filtered,  and  the  filtrate  boiled 
for  some  time.  If  a  precipitate  is  formed  which 
disappears  again,  on  cooling,  tartaric  acid  is  present. 
Solution  of  gypsum  is  added  to  a  portion  of  the 
original  solution,  which,  if  acid,  must  first  be  made 
neutral  by  the  addition  of  ammonia.  The  formation 
of  a  precipitate,  which  does  not  disappear  upon  the 
addition  of  acetic  acid,  but  is  dissolved  by  hydrochlo- 
ric acid,  indicates  OXALIC  ACID. 

8.  The  fluid  in  which  chloride  of  calcium  has  produced 
no  precipitate,  or  that  which  has  been  filtered  off  from 
the  precipitate  formed — (in  which  latter  case  some  more 
chloride  of  calcium  is  added) — is  mixed  with  alcohol. 

a.  No  PRECIPITATE  is  FORMED.     Absence  of  citric 
acid  and  of  malic  acid.    Pass  over  to  9. 


PRESENCE    OF   ORGANIC    ACIDS.  241 

b.  A  PRECIPITATE  is  FORMED.  The  solution  is 
filtered  off  and  the  filtrate  treated  as  9  directs.  The 
precipitate  is  washed  with  alcohol,  and  (being  left  on 
the  filter)  dissolved  in  the  least  possible  quantity  of 
dilute  hydrochloric  acid.  Ammonia  is  then  added  to 
this  latter  filtrate,  till  it  manifests  a  feebly  alkaline 
reaction,  and  heat  applied  to  the  boiling  point,  at 
which  it  must  be  kept  for  some.  time. 

*.    THE  FILTRATE  REMAINS  CLEAR.       Absence   of 

citric  acid.  Presence  of  MALIC  ACID  ;  alcohol  is 
again  added  to  the  fluid,  and  the  lime  precipitate 
which  is  formed,  heated  to  redness,  as  a  conclu- 
sive test  for  malic  acid  ;  the  reaction  with  acetate  of 
lead  is  moreover  resorted  to  as  a  confirmatory  proof, 
§  102,  e,  5. 

/3.    A    HEAVY,      WHITE    PRECIPITATE    IS    FORMED. 

Presence  of  CITRIC  ACID.  The  solution  is  filtered 
whilst  boiling,  and  the  filtrate  tested  for  malic  acid, 
as  described  at  *. 

9.  Perchloride  of  iron  is  added  to  the  filtrate  of  8,  6,  or 
to  the  fluid,  in  which  no  precipitate  has  been  formed,  on 
mixing  with  alcohol,  (§  128,  8,  a,)  after  having  previously 
expelled  the  alcohol  by  heat,  and  after  having  exactly  neu- 
tralized with  hydrochloric  acid.  If  no  light  brown  floccu- 
lent  precipitate  is  formed,  neither  succinic  acid  nor  benzoic 
acid  are  present ;  if  a  precipitate  of  this  kind  is  formed, 
and  no  benzoic  acid  has  been  detected  during  the  previous 
examination,  (§  124,  2,)  this  consists  of  SUCCINIC  ACID. 
But  if  benzoic  acid  was  present,  the  solution  is  filtered  off, 
and  the  precipitate  washed  and  then  digested  with  ammo- 
nia in  excess,  filtered,  the  filtrate  evaporated  to  dryness, 
and  the  benzoate  of  ammonia  dissolved  out  of  it  by  alco- 
hol ;  the  succinate  of  ammonia  remains  undissolved.  This 
succinate  is  dissolved  in  water,  and  both  solutions  are 
tested  with  perchloride  of  iron. 

10.  Test  for  NITRIC  ACID  as  directed  §  123. 

Compounds  in  which  all  the  more  frequently  occurring 
bases,  acids,  metals,  and  metalloids,  are  supposed  to  be 
present. 


242  ABSENCE  OP    ORGANIC    ACIDS. 

A.  2.  SUBSTANCES  INSOLUBLE  IN  WATER,  BUT  SOLUBLE  IN 

HYDROCHLORIC   ACID  AND  IN  NITRIC   ACID.       DETECTION 
OF  THE  ACIDS  AND  METALLOIDS. 

I.  Absence  of  Organic  Acids. 
§  125. 

In  examining  these  compounds  we  must  look  for  all  the 
acids  occurring  at  §  123,  with  the  exception  of  chloric 
acid.  Cyanogen  compounds  are  not  examined  after  this 
method:  compare  §  128. 

1 .  What  we  have  stated  at  §  111,  2,  with  regard  to  AR- 
SENIOUS  and  ARSENIC  ACID,  HYDROSULPHURIC  ACID    and 
CHROMIC  ACID,  applies  also  to  this  paragraph. 

2.  A  portion  of  the  substance  is  boiled  with  nitric  acid, 
and  the  solution  filtered,  should  any  residue  remain. 

a.  Effervescence  takes  place ;  this  may  be  caused 
by  the  presence  of  CARBONIC  ACID,  or  by  that  of  NI- 
TRIC OXIDE  GAS  ;  the  former  may  be  detected  as  §  99, 
«,  directs,  the  latter  usually  indicates  the  presence  of 
a  sulphur  compound. 

b.  Violet  vapours  escape,  which  impart  a  blue  tint 
to  starch:   IODINE. 

3-  Nitrate  of  silver  is  added  to  a  portion  of  the  nitric 
solution. 

<z.  No  PRECIPITATE  is  FORMED  :  pass  over  to  4,  for 
no  chlorine  is  present. 

b.  A  PRECIPITATE  is  FORMED.  The  solution  is  fil- 
tered off,  and  the  precipitate  washed,  and  digested 
with  ammonia  ;  if  it  redissolves  completely  or  partly, 
CHLORINE  is  present. 

4.  A  portion  of  the  substance  under  examination  is  boiled 
with  hydrochloric  acid,  and  the  solution  filtered,  if  necessary. 
A  portion  of  the  solution  or  filtrate  is  mixed  with  chloride 
of  barium.     The  formation  of  a  precipitate  indicates  SUL- 
PHURIC ACID. 

5.  Another  portion  of  the  hydrochloric  solution  is  test- 
ed for  NITRIC  ACID,  with  indigo  and  protosulphate  of  iron. 
(Vide  §  1 23,  4.)   In  many  cases  it  will  already  have  been  de- 
tected by  the  deflagration  on  charcoal  before  the  blow- 
pipe. 

6.  If  the  experiment,  §  125,  2,  6,  has  not  yet  indicated 
the  presence  of  iodine,  a  portion  of  the  substance  under  ex- 


PRESENCE    OF    ORGANIC    ACIDS.  243 

animation  is  heated  with  concentrated  sulphuric  acid.  If 
any  IODINE  compound  be  present,  violet  vapours  will  be 
evolved,  which  impart  a  blue  tint  to  starch.  (Compare  § 
100,  c,  6.) 

7.  Test  for  BORACIC  ACID  by  treating  a  portion    of  the 
substance  to  be   examined  with  sulphuric  acid  and  alco- 
hol.    (Vide  §  98,  b,  5.) 

8.  The  fluid  of  §  119,  «,  (in  which  phosphate  of  soda 
produces  no  precipitate,)  or  that  of  §  119,  1,  (in  which  car- 
bonate of  ammonia  produces  no  precipitate,)  or— (should 
carbonate  of  ammonia  have  produced  a  precipitate  in  it) — 
the  nitrate  of  the  same  (§  119,  2,)  (vide  §  121,)  are  tested 
for  PHOSPHORIC  ACID  and  OXALIC  ACID,  as  directed  §  123, 

5,  and  9.      (Oxalic   acid,  when   combined  with  barytes, 
strontian,  or  lime,  will  have  been  detected  already,  in  test- 
ing for  the  bases ;    the  same  applies   to  phosphoric    acid 
when  combined  with  magnesia.) 

9.  Test  for  SILICIC  ACID  as  §  99,  b,  3,  directs.     With 
regard  to  the  more  rarely  occurring  BROMINE  and  FLUORINE 
compounds,  we  refer  to  the   remarks  made  at  the  end  of 
§  123. 

Compounds  in  which  all  the  more  frequently  occurring 
bases,  acids,  metahj  and  metalloids,  are  supposed  to 
be  present. 

A.  2.  SUBSTANCES  INSOLUBLE  IN  WATER,  BUT  SOLUBLE  IN 

HYDROCHLORIC    ACID,     AND    IN    NITRIC      ACID.        DETEC- 
TION OF  THE  ACIDS  AND  METALLOIDS. 

II.  Presence  of  Organic  Acids. 
§  126. 

1.  Test  for  CARBONIC  ACID,  ARSENIC  ACID,  ARSENIOUS 

ACID,  SULPHURIC  ACID,  NITRIC  ACID,  BORACIC  ACID,  CHRO- 
MIC ACIDj  SILICIC  ACID,  CHLORINE,  IODINE,  and  SULPHUR, 

as  directed  at  §  125  ;    for  ACETIC  ACID  as  stated  at  §  124, 

6.  CYANOGEN  compounds  are  not   examined   after  this 
method:  compare  §  128. 

2.  A  portion  of  the  compound  under  examination  is  dis- 


244  INSOLUBLE  SUBSTANCES. 

solved  in  hydrochloric  acid,  and  the  solution  filtered,  should 
any  residue  remain,  (which  latter  is  tested  for  BENZOIC 
ACID,  as  directed  at  §  124,  2.)  The  filtrate  is  mixed  with 
solution  of  carbonate  of  potash,  and  the  mixture  boiled  for 
some  time.  The  fluid  is  filtered  off  from  the  precipitate 
formed,  and  the  filtrate  saturated  with  dilute  hydrochloric 
acid,  and  tested  for  PHOSPHORIC  ACID  and  OXALIC  ACID,  as 
directed  at  §  123,  5,  and  9  ;  and  for  TARTARIC  ACID,  CITRIC 

ACID,  MALIC  ACID,  SUCCINIC  ACID  and  BENZOIC  ACID,  CXaCt- 

ly  as  directed  at  §  124,  7,  8,  and  9. 

Compounds  in  which  all  the  more  frequently  occurring 
bases,  acids,  metals,  and  metalloids,  are  supposed  to 
be  present. 

B.  SUBSTANCES  INSOLUBLE  OR  SPARINGLY  SOLUBLE  BOTH 

IN    WATER    AND     IN    HYDROCHLORIC    ACID.       DETECTION 
OF    THE    BASES,   ACIDS,    AND    METALLOIDS. 

§     127. 

The  following  substances  and  combinations  belong  to 
this  class  : 

SULPHATE  OF  BARYTES,  SULPHATE  OF  STRONTIAN,  SUL- 
PHATE OF  LIME,  CHLORIDE  OF  SILVER,  CHLORIDE  OF  LEAD, 
SULPHATE  OF  LEAD,  SULPHURET  OF  MERCURY,  BISUL- 
PHURET  OF  MERCURY,  PROTOCHLORIDE  OF  MERCURY, 
SOME  OF  THE  FERROCYANIDES,  SEVERAL  SULPHURETS, 
SILICIC  ACID,  SULPHUR  and  CARBON. 

Besides  these,  a  few  acid  arseniates  belong  to  this  class  ; 
they  are,  however,  as  rarely  occurring  in  the  analyses  of 
those  mixtures  and  compounds  important  in  pharmacy, 
manufacture,  arts,  and  trades,  as  the  insoluble  modification 
of  oxide  of  chromium,  or  as  roasted  peroxide  of  tin,  or  as 
fluoride  of  calcium.  Of  these  latter  less  frequently  oc- 
curring substances^  we  purpose  to  treat  separately. 

For  the  insoluble  cyanides,  vide  §  128. 

A.  THE  RESIDUE  is  WHITE.  It  may  in  that  case  con- 
tain SULPHATE  OF  BARYTES,  SULPHATE  OF  STRONTIAN, 
SULPHATE  OF  LIME,  SULPHATE  OF  LEAD,  CHLORIDE  OF 
LEAD,  CHLORIDE  OF  SILVER,  PROTOCHLORIDE  OF  MERCURY, 
SILICIC  ACID,  SULPHUR. 


PRESENCE    OF    ORGANIC    ACIDS.  245 

No  attention  need  be  paid  to  the  presence  of  sulphate  of 
lime,  if  this  substance  lias  already  been  detected  in  the 
aqueous  solution.  The  same  remark  applies  to  the  lead 
compounds  :  we  may  disregard  these,  if  the  previous  ex- 
amination has  not  already  proved  their  presence. 

1.  A  small  portion  of  the  substance  under  examination 
is  heated  upon  a  platinum  plate,  and  flame  allowed  to  play 
on  it.     If  any  odour  of  sulphurous  acid  is  emitted,  SUL- 
PHUR is  present.     If  no  residue  remains,  sulphur  alone  is 
present.     If  the  heat  applied  was  very  intense,  protochlo- 
ride  of  mercury  may  have  volatilized.     The  sensible  pro- 
perties of  the  residue  will  show  whether  this  is  to  be  ap- 
prehended. 

2.  Hydrosulphuret  of  ammonia  is  added  to  a  very  small 
portion  of  the  substance  under  examination. 

a.  It  remains  white.    Pass  over  to  §  127,  3,  for  no 
metallic  compounds  are  present. 

b.  It  becomes  black.     This  proves  with  certainty 
the  presence  of  a  metallic  salt,  either  protochloride 
of  mercury,   chloride   of  silver,  chloride  of   lead,    or 
sulphate    of    lead.     Moreover,    all   the   other   com- 
pounds enumerated  under  A,  may  be  present.     The 
method  of  the  further  operation  varies  according  to 
whether  lead  is  present  or  not. 

The  following  preliminary  experiment  is  made  in 
order  to  ascertain  which  method  ought  to  be  adopted. 

A  small  portion  of  the  substance  is  mixed  with 
carbonate  of  soda,  and  exposed  to  the  reducing  flame 
of  the  blow-pipe.  The  production  of  a  metallic 
grain,  (which  oxidizes  in  the  oxidizing  flame,)  at- 
tended with  a  yellow  incrustation  of  the  charcoal,  in- 
dicates lead. 

*.  THIS  PRELIMINARY  EXAMINATION  INDICATES 
THE  PRESENCE  OF  LEAD  IN  THE  WHITE  PRECIPI- 
TATE. 

aa.  The  largest  half  of  the  residue  (which,  if 
moist,  must  first  be  dried)  is  fused  with  three 
parts  of  dry  carbonate  of  soda  and  three  parts  of 
cyanide  of  potassium,  in  a  small  crucible,  over  a 
spirit-lamp.  The  mass  fuses  easily ;  it  is  main- 
tained in  a  state  of  fusion  for  some  time.  After 


246  PRESENCE  OP    ORGANIC    ACIDS. 

cooling,  it  is  boiled  with  water,  filtered,  and  the 
residue  very  carefully  washed.  The  greater 
portion  of  the  filtrate  is  supersaturated  with 
hydrochloric  acid,  and  a  portion  of  this  solution 
tested  with  chloride  of  barium.  The  formation 
of  a  precipitate  indicates  the  presence  of  a  SUL- 
PHATE. (Should  a  precipitate  (silicic  acid)  be 
formed,  upon  supersaturating  the  filtrate  with 
hydrochloric  acid,  the  fluid  must  be  diluted  and 
filtered,  and  then  tested  for  sulphuric  acid.)  The 
rest  of  the  solution  (supersaturated  with  hydro- 
chloric acid)  is  evaporated  to  dryness  and  the 
residue  treated  with  water.  If  a  residue  remains, 
this  consists  of  SILICIC  ACID.  The  formation 
of  a  clear  glass,  when  fused  with  carbonate  of 
soda  in  the  blow-pipe  flame,  is  a  conclusive 
proof  of  the  presence  of  silicic  acid.  The  rest 
of  the  filtrate,  which  has  not  been  mixed  with 
hydrochloric  acid,  is  acidified  with  nitric  acid, 
boiled  until  it  emits  no  longer  any  odour  of 
hydrochloric  acid,  and  nitrate  of  silver  added  ; 
the  formation  of  a  precipitate  of  chloride  of  silver 
denotes  that  the  residue,  insoluble  in  water  and 
hydrochloric  acid,  contains  a  CHLORIDE,  (pro- 
vided always,  the  reagents  be  free  from  chlorine, 
and  the  residue  completely  washed.)  The  resi- 
due obtained  upon  treating  the  fused  ma'ss  with 
water,  and  which  has  been  very  carefully  washed, 
(vide  supra,)  is  treated  with  acetic  acid ;  if  it 
partly  dissolves  in  this  acid  with  effervescence, 
the  presence  of  sulphates  of  the  alkaline  earths 
is  certain.  If  no  effervescence  takes  place,  it 
proves  the  absence  of  the  sulphates  of  the  alka- 
line earths ;  the  residue  is  therefore  treated  with 
nitric  acid,  and  the  solution  treated  as  follows. 
If  effervescence  has  taken  place,  a  portion  of  the 
acetic  solution  is  tested  with  sulphuretted  hydro- 
gen. If  a  black  precipitate  is  formed,  (sulphuret 
of  lead,)  the  lead  is  removed  in  the  same  man- 
ner from  the  entire  acetic  solution,  and  the  fil- 
trate (which,  if  necessary,  is  concentrated  by 


PRESENCE    OP    ORGANIC    ACIDS.  247 

evaporation)  treated  as  §  119  directs,  beginning 
at  2,  #.  If  the  test  portion  of  the  acetic  solution 
remains  unaltered  upon  being  treated  with  sul- 
phuretted hydrogen,  the  rest  of  the  solution  is 
directly  tested  as  directed,  §  119,  2,  a.  The  re- 
sidue, which  has  remained  on  treating  with  the 
acetic  acid,  is  treated  with  nitric  acid,  and  a 
small  portion  of  the  solution  is  then  tested  with 
sulphuric  acid  for  lead,  (after  having  removed 
the  excess  of  acid  by  evaporation;)  the  rest 
strongly  diluted  with  water,  and  then  tested  for 
SILVER,  with  hydrochloric  acid.  If  nitric  acid 
leaves  a  residue,  this  consists  of  undissolved  si- 
licic acid,  or  incompletely  decomposed  sulphate 
of  the  alkaline  earths, 

bb.  Half  of  the  remainder  of  the  residue  is 
boiled  with  carbonate  of  potash.  If  its  white 
colour  change  into  gray  or  black,  PROTOCHLO- 
RIDE  OF  MERCURY  is  present.  As  a  confirmatory 
test  the  other  half  is  heated  in  a  small  glass  tube, 
together  with  dry  carbonate  of  soda.  (Vide  §  90, 
6,7.) 

/3.    THE  PRELIMINARY  EXAMINATION  PROVES  THE 
ABSSNCE    OF     LEAD,   IN    THE     WHITE     PRECIPITATE. 

The  entire  entire  residue  is  drenched  and  digested 
for  some  time,  with  hydrosulphuret  of  ammonia, 
the  solution  filtered,  and  the  filtrate  tested  for  chlo- 
rine, as  aa  directs.  The  precipitate  is  washed  and 
boiled  with  nitric  acid. 

aa.  The  precipitate  dissolves  with  the  excep- 
tion of  the  separated  sulphur.  CHLORIDE  OF 
SILVER  alone  is  present.  To  assure  ourselves, 
we  test  the  nitric  solution  for  silver,  with  hydro- 
chloric acid.  To  prove  the  presence  of  chlorine, 
the  filtrate  of  §  127,  A,  2,  £,  is  supersaturated 
with  nitric  acid,  and  boiled,  in  order  to  expel  the 
sulphuretted  hydrogen.  The  fluid  is  then  filtered 
from  the  sulphur  which  has  separated,  and  tested 
with  nitrate  of  silver. 

bb.  A  residue  remains  besides  the  separated 
sulphur. 


248  INSOLUBLE  SUBSTANCES. 

«-*.  This  residue  is  black:  MERCURY.  The 
fluid  is  filtered  from  the  residue,  and  the  fil- 
trate tested  for  silver,  with  hydrochloric  acid : 
the  residue  is  heated  with  aqua  regia.  If  it  is 
completely  redissolved,  with  the  exception  of 
the  separated  sulphur,  the  investigation  may 
be  considered  at  an  end,  the  absence  of  the 
sulphates  of  the  alkaline  earths  and  that  of  sili- 
cic acid  being  proved;  if  a  white  residue 
remains,  this  is  washed  and  treated  as  §  127, 
A,  3,  directs.  The  solution  in  aqua  regia 
is  tested  with  polished  copper  or  with  pro- 
tochloride  of  tin  to  assure  ourselves  of  the 
presence  of  mercury,  (vide  §  117,  2.)  The 
chlorine,  which  must  be  present,  is  detected  in 
the  filtrate  of  /3,  as  aa  directs. 

/3/3.  THE  RESIDUE  is  NOT  BLACK  :  absence 
of  mercury.  For  the  further  operation  vide  3. 

3.  This  residue,  or,  in  the  case  of  §  127,  A,  2,  a,  the  ori- 
ginal residue  is  fused  in  a  platinum  crucible,*  over  a' spirit 
lamp  with  a  double  draught  of  air,  together  with  four  parts 
of  carbonate  of  potash  and  soda  ;  the  fused  mass  is  soaked 
in  water,  boiled,  filtered,  and  the  residue  (if  any  remain) 
washed  until  chloride  of  barium  no  longer  produces  any 
precipitate  in  the  water,  which  runs  off.     (This  water  must 
not  be  added  to  the  filtrate.      The  residue  is  treated  as  4 
directs.     The  filtrate   is  supersaturated  with  hydrochloric 
acid,  and  a  portion  of   it  tested  with  chloride  of  barium ; 
the  formation  of  a  precipitate  indicates  the  presence  of 

SULPHATES    OF    THE    ALKALINE    EARTHS.       The    TCSt  of  the 

filtrate  is  evaporated  to  dryness  and  then  treated  with  water; 
if  any  residue  remains,  this  consists  of  SILICIC  ACID. 

4.  The    residue    remaining   upon   boiling    the    fused 
mass    with    water,    (vide    3,)    indicates    SULPHATES    OF 
THE  ALKALINE  EARTHS.     It  is  carefully  washed  and  then 
treated   with  hydrochloric   acid.       It  is  a   certain  proof 
of  the  presence  of  sulphates  of  the   alkaline  earths,   if 
it  dissolves  partly  or  totally,    and  with  effervescence  in 

*  A  porcelain  crucible  may  be  substituted  for  a  platinum  crucible,  in 
which  case,  six  parts  of  a  mixture  of  equal  parts  of  dry  carbonate  of  soda 
and  cyanide  of  potassium  must  be  employed,  instead  of  the  carbonate  of 
potash  and  soda ;  the  method  in  the  text  is  however  the  best. 


PRESENCE    OP    ORGANIC    ACIDS.  249 

this  menstruum.  The  hydrochloric  solution  is  tested 
as  §  119  directs,  beginning  at  2,  a.  If  a  residue  remains 
upon  treating  with  hydrochloric  acid,  this  consists  of 
silicic  acid  or  of  a  sulphate  of  the  alkaline  earths  which 
is  not  yet  completely  decomposed. 

B.  THE  RESIDUE  is  NOT  WHITE.  Even  its  colour  will 
in  that  case  enable  us  to  draw  some  conclusions  (cinnibar, 
sulphuret  of  arsenic.) 

1.  Test  for  SULPHUR  as  §  127,  A,  1,  directs. 

2.  The  greater  part  of  the  residue  is  treated  with  aqua 
regia  and  boiled ;  the  solution  is  filtered  whilst  still  hot, 
and  should  any  residue  remain,  besides  the  separated  sul- 
phur, this  is  once  more  boiled  with  water,  filtered,  and  this 
second  filtrate  added  to  the  first.     The  filtrate  is  then  eva- 
porated nearly  to  dryness,  redissolved  in  some  water,  and 
one  portion  of  the  solution  tested  for  LEAD,  with  sulphuric 
acid,  another  portion  for  MERCURY  by  means  of  polished 
copper.     (If  a  hydrochloric  solution  has  been  employed  in 
testing  for  bases,  (§  106,)  the   solution  in  aqua  regia  must 
be  tested  for  metals,  in  the  usual  way,   as  various  other 
sulphurets,  insoluble  or  sparingly  soluble  in  hydrochloric 
acid,  might  be  present.) 

3.  If  aqua  regia  has  left  any  residue  undissolved  besides 
sulphur,  which  may  have  separated,  this  residue  is  careful- 
ly washed.     If  a  compound  of  lead  has  been  present,  this 
rinsing  process  is  conducted  with  hot  water  and  continued 
until  the  filtrate  is  no  longer  blackened  by  hydrosulphuret 
of  ammonia. 

a.  THE  RESIDUE  is  WHITE  :  a  portion  of  it  is  tested 
with  hydrosulphuret  of  ammonia. 

«.  It  becomes  black.  The  entire  residue  is  digest- 
ed with  hydrosulphuret  of  ammonia,  and  the  further 
operation  conducted  exactly  as  §  127,  A,  2,  6,  /3, 
directs. 

$.  It  remains  white.  The  residue  is  treated  as 
directed  §  127,  A,  3. 

6.  THE  RESIDUE  INSOLUBLE    IN  AQUA    REGIA,    is 
BLACK  ;  this  indicates  the  presence  of  carbon  in  some 
form.     If  it  is  totally  consumed  over  a  lamp,  or  in  the  blow- 
pipe flame,  nothing  besides  carbon  is  present ;  but  if  a  res- 
idue remains,  or  if  the  combustion  is  not  complete,  (carbu- 


250  METHOD    WITH    INSOLUBLE    CYANIDES. 

ret  of  iron  graphyte,)  we  must  look  moreover  for  CHLORIDE 

OF     SILVER,    SULPHATES      OF     THE     ALKALINE    EARTHS    and 

SILICIC  ACID  ;  the  residue  in  that  case,  is  treated  as  §  127, 
B,  3,  a,  *,  directs.  Of  acids  and  electro-negative  substan- 
ces CHLORINE  and  SULPHURIC  ACID  alone  can  be  present 
besides  those  already  mentioned.  To  assure  ouselves 
whether  they  are  present  or  not,  what  remains  of  the  resi- 
due insoluble  in  hydrochloric  acid  is  digested  with  hydro- 
sulphuret  of  ammonia,  super-saturated,  filtered,  and  one-half 
of  the  filtrate  boiled  with  hydrochloric  acid,  the  other  half 
with  nitric  acid  ;  both  solutions  are  filtered  and  the  hydro- 
chloric fluid  is  tested  with  chloride  of  barium  for  sulphuric 
acid,  the  nitric  fluid  with  nitrate  of  silver  for  chlorine. 

The  insoluble  PEROXIDE  OF  TIN  and  OXIDE  OF 
CHROMIUM  may  be  detected  before  the  blow-pipe. 
Peroxide  of  tin,  when  mixed  with  carbonate  of  soda 
and  cyanide  of  potassium,  and  exposed  on  charcoal 
to  the  reducing  flame  of  the  blow-pipe,  yields  a  soft 
metallic  grain,  without  incrustation  of  the  support. 
Oxide  of  chromium,  which  is,  moreover,  distinguished 
by  its  green  colour,  is  treated  with  microcosmic  salt, 
as  stated  §  87,  6,  5,  or  it  is  fused  together  with  car- 
bonate of  soda  and  nitre,  (vide  §  87,  b,  4.)  The 
arsenic  acid  of  the  insoluble  ARSENIATES  is  detected 
before  the  blow-pipe  or  by  means  of  reduction  in  a 
glass  tube.  (Vide  §  94,  d.}  To  enable  us  to  test  for 
the  bases,  these  insoluble  arseniates  must  first  be 
decomposed  by  means  of  concentrated  sulphuric  acid. 
FLUORIDE  OF  CALCIUM  is  decomposed  by  concentrated 
sulphuric  acid,  in  a  platinum  crucible  :  the  fluorine  is 
detected  by  its  property  of  etching  glass  ;  the  lime 
remains  as  sulphate  of  lime.  There  are  still  several 
other  compounds  which  are  rendered  insoluble  in 
acids  by  being  heated  to  redness  ;  but  it  would  exceed 
the  limits  of  this  work,  to  treat  of  them  all. 


METHOD   WITH   INSOLUBLE    CYANIDES.  251 

§128. 

SPECIAL    METHOD   FOR    THE    DECOMPOSITION    OF    INSOLUBLE 
CYANIDES,   FERROCYANIDES,    &C.* 

Since  in  treating  these  compounds  according  to  the 
usual  method,  fallacious  phenomena  frequently  occur,  and 
since  moreover  their  solution  in  acids  frequently  succeeds 
but  imperfectly,  it  is  advisable  to  pursue  the  following 
method,  in  their  analysis.  The  residue  which  has  been 
freed  by  water  from,  all  soluble  substances  is  boiled  with 
solution  of  carbonate  of  potash. 

a.  COMPLETE  DECOMPOSITION  TAKES  PLACE,  which 
is  easily  detected  by  the  change  of  colour  and  the 
rapid  deposition  of  the  separated  pure  or  carbonated 
oxides  ;  the  solution  is  filtered  and  the  residue  washed. 
This  residue  may  contain  all  the  bases,  which  were 
contained  in  the  substance  under  examination  as  com- 
pounds insoluble  in  water.  For  the  determination  of 
these  bases,  the  residue  is  treated  exactly  as  §  106, 
A,  2,  directs.  A  portion  of  the  filtrate  is  tested  for 
CYANOGEN,  by  mixing  it  with  hydrochloric  acid,  till 
the  reaction  becomes  strongly  acid,  and  then  adding 
solution  of  the  double  proto-  and  per-chloride  of  iron ; 
if  cyanogen  be  present,  Prussian  blue  precipitates. 
For  the  detection  of  the  other  acids,  the  rest  of  the 
filtrate  is  treated  as  §  124  directs.  This  filtrate  may, 
moreover,  possibly  contain  all  the  cobalt,  all  the  iron 
of  the  substance  under  examination,  besides  chromium 
and  manganese,  since  the  combinations  of  their  cya- 
nides with  other  cyanogen  compounds,  on  boiling 
with  alkalies,  are  decomposed  in  such  a  manner  as 
to  cause  the  separation  of  insoluble  oxides,  whilst  the 
cobalticyanide  of  potassium,  ferrocyanide  of  potas- 
sium, &c.,  remain  in  solution.  These  metals  must 
not  be  disregarded.  To  detect  them,  a  portion  of  the 
fluid  is  mixed  with  nitric  acid  greatly  in  excess,  the 
mixture  evaporated  to  dryness  and  the  residue  fused ; 


*  The  student  is  advised  to  read  the  additional  remarks  to  §  128,  con- 
tained in  the  second  chapter,  previous  to  entering  upon  this  method  of 


252  PRESENCE    OF   ORGANIC   MATTER. 

should  the  quantity  of  the  nitre  formed  not  be  suffi- 
cient, some  must  be  added  whilst  fusing  the  residue. 
The  metals,  with  the  exception  of  chromium,  remain 
as  oxides,  and  are  separated  and  detected  according 
to  the  methods  given  above.  The  chromium  is  ob- 
tained as  soluble  chromate  of  potash. 

b*    No  COMPLETE  DECOMPOSITION  TAKES  PLACE  I  Caustic 

potash  is  added  and  the  mixture  boiled.  Should  any 
residue  remain,  this  is  filtered,  after  the  previous 
addition  of  some  water,  and  then  dissolved  and  treated 
as  §  106,  A,  2,  directs.  The  alkaline  filtrate  is  satu- 
rated with  sulphuretted  hydrogen.  If  any  precipitate 
be  formed,  this  is  again  filtered,  dissolved  in  nitric 
acid,  and  the  solution  treated  as  §  114,111.  directs. 
The  filtrated  liquor  is  slightly  acidified  .with  hydro- 
chloric acid  and  sulphuretted  hydrogen  added  should 
it  appear  necessary.  If  a  precipitate  be  formed,  this 
is  treated  as  §  116  directs.  The  filtrate  is  tested  for 
cyanogen  and  the  other  electro-negative  bodies,  and 
acids,  and  for  cobalt,  iron,  manganese,  and  chromium, 
as  §  128,  a,  directs.  (When  fusing  the  residue  with 
nitre,  according  to  the  method  laid  down  in  §  128,  «, 
(vide  this  section  from  the  words,  "  These  metals 
must  not  be  disregarded,"  to  the  end,)  besides  the 
oxides,  alumina  is  obtained,  if  any  be  present ;  this 
must  be  borne  in  mind.) 

§  129. 

GENERAL  RULES  FOR  THE  DETECTION  OF  INORGANIC  SUB- 
STANCES J  IN  CASES  WHERE  ORGANIC  SUBSTANCES  ARE 
PRESENT,  WHICH  BY  THEIR  COLOUR,  CONSISTENCE,  OR 
OTHER  PROPERTIES,  IMPEDE  THE  APPLICATION  OF  THE 
REAGENTS,  OR  RENDER  THE  PHENOMENA  OBSCURE. 

We  have  already  stated  in  our  introductory  remarks, 
that  cases  of  this  kind  are  so  manifold,  that  it  is  impossi- 
ble to  lay  down  a  determinate  method  for  every  especial 
case;  we  must,  therefore,  content  ourselves  with  giving 
only  such  methods  as  are  applicable  in  most  cases,  and 
leaving  it  to  the  judgment  of  the  operator  to  adopt  those 
modifications  which  he  may  deem  necessary. 


PRESENCE    OF    ORGANIC   MATTER.  253 

1.  THE  SUBSTANCE  DISSOLVES  IN  WATER,  BUT  IS  OF  A  DARK 
COLOUR   OR  .HAS  A  SLIMY  CONSISTENCE. 

a.  One  part  of  the  solution  is  boiled  with  hydro- 
chloric acid,  and  chlorate  of  potash  gradually  added 
till  the  fluid  has  become  discoloured  and  limpid  j  the 
solution  is  then  heated  until  all  odour  of  chlorine  has 
disappeared,  diluted  with  water,  and  filtered.  The 
filtrate  is  treated  after  the  usual  method,  beginning  at 
§  115°. 

b*  Another  portion  of  the  solution  is  boiled  for 
some  time  with  nitric  acid,*  filtered,  and  the  filtrate 
tested  for  silver,  potash,  and  hydrochloric  acid.  This 
kind  of  treatment  is  frequently  preferable  to  all  others 
in  such  cases  where  the  destruction  of  the  colouring, 
slimy  matters,  &c.,  succeeds  well  by  means  of  nitric 
acid. 

2,  The  body  does  not  dissolve  in  boiling  water,  or  dis- 
solves only  in  part.  The  solution  is  filtered,  and  the  filtrate 
treated  either  as  §114  directs,  or,  if  it  be  necessary  to 
destroy  the  colouring  matters  which  it  may  contain  in  ad- 
mixture, as  directed  §  129,  I.     If  it  is  impossible  to  filter 
the  solution,  the  further  operation  must  be  conducted  as 
stated  §  129,  2,  c.     The  nature  of  the  residue  may  be 
various,  • 

a.  IT  is  GREASY.     The  fatty  matters  are  removed 
by  means  of  ether,  and  should  any  residue  remain,  this 
is  treated  as  §  106  directs. 

b.  IT  is  RESINOUS.     Alcohol  is  employed  instead 
of  ether,  or  a  mixture  of  both  liquids  is  used. 

c.  IT  is  OF  ANOTHER  NATURE,  c.  g.  organic  fibrine, 
&c.     The  residue  insoluble  in  water  is  dried,  and  the 
greater  part  of  it  rubbed  together  with  from  three  to 
four  parts  of  pure   nitre  ;  the  mixture  is  gradually- 
deflagrated  in  a  red  hot  crucible.     The  residue  is 
treated  as  §  106,  A,  directs.     Another  part  is  boiled 
with  aqua  regia,  the  solution  filtered  and  the  filtrate 
tested  for  mercury.     The  rest  is  tested  for  ammonia, 
as  §  122  directs. 

11 


254:  NOTES  AND  ADDITIONS,  ETC. 

§130. 

IV.  k  CONFIRMATORY  EXPERIMENTS. 

When  the  various  bases,  acids,  and  electro-negative 
bodies,  present  in  the  substance  under  examination  have 
been  detected,  it  is,  in  many  cases,  advisable,  in  others 
absolutely  necessary,  to  verify  our  conclusions.  In  many 
cases  this  is  easily  accomplished,  since  certain  substances 
have  such  characteristic  reactions  that  their  presence  or 
absence  may  at  once  be  determined,  although  many  other 
substances  are  present  at  the  same  time.  But  many  sub- 
stances have  not  such  characteristic  reactions,  in  which 
cases  we  must  satisfy  ourselves  by  a  strict  and  minute 
examination,  and  by  varying  our  processes,  determine 
whether  the  phenomena  usually  indicating  the  presence 
of  a  substance,  do  not  proceed  from  extraneous  causes. 

Thus  ammonia  may  be  erroneously  supposed  to  be  pre- 
sent in  a  substance,  whilst  it  is  in  fact  derived  from  the 
atmosphere  of  the  laboratory,  &c. 

In  the  course  of  this  work  we  have  pointed  out  those 
reactions  which  may  be  sought  as  confirmatory  proofs, 
and  the  precautions  necessary  to  secure  the  purity  of  our 
reagents. 


CHAPTER  II. 

EXPLANATORY  NOTES  AND  ADDITIONS   TO   THE 
PRACTICAL  COURSE. 

I.  REMARKS  ON  THE  PRELIMINARY  EXAMINATION. 
§105. 

THE  sensible  qualities  of  bodies,  as  I  before  remarked, 
may  often  enable  us  at  once  to  deduce  certain  general  con- 
clusions, as  to  their  nature,  at  least  negatively.  Thus,  a 
white  powder  cannot  «be  cinnabar,  a  light  flocculent  body 


ADDITIONAL  REMARKS.    .  255 

cannot  be  a  compound  of  lead,  &c.  But  the  student  must 
beware  of  forming  opinions  prematurely,  respecting  the 
nature  of  a  body  from  its  sensible  properties  only,  lest  it 
give  rise  to  such  preconceptions  as  may  lead  him. to  draw 
fallacious  conclusions  from  the  reactions  which  manifest 
themselves  afterwards  in  the  course  of  the  real  exam- 
ination. 

In  the  examination  of  bodies,  at  a  high  temperature, 
small  glass  tubes  may  be  often  advantageously  substituted 
for  a  metallic  spoon,  since  they  enable  us  to  observe  any 
substance  which  may  volatilize  in  the  process  ;  but  as  a 
new  tube  is  needed  in  every  experiment,  the  metallic 
spoons  may  serve  in  ordinary  practice. 

With  respect  to  the  blow-pipe  examination,  the  student 
must  avoid  drawing  positive  conclusions  until  he  has  ac- 
quired a  certain  degree  of  experience,  from  practice ;  a 
slight  incrustation  may  not  imply  the  presence  of  a  metal, 
nor  his  inability  to  effect  a  reduction  or  to  produce  a  colour 
by  solution  of  cobalt,  the  absence  of  a  substance  sought. 
The  blow-pipe  phenomena  are,  indeed,  in  most  cases 
unerring,  but  they  are  easily  modified  by  adventitious 
circumstances. 

The  preliminary  examination  is  in  no  case  to  be  passed 
over  by  the  student. 

II.  ADDITIONAL  REMARKS  UPON  SOLUTION,  &c. 
§  106. 

There  is  some  difficulty  in  determining  the  limits  of  the 
two  classes  of  bodies,  soluble  and  insoluble,  since  these 
terms  are  but  relative,  and  we  use  the  phrases  easily,  and 
sparingly,  or  difficultly  soluble  ;  and,  indeed,  these  two 
classes  merge  into  each  other.  Sulphate  of  lime  which 
is  soluble  in  four  hundred  and  sixty-one  parts  of  water 
might  perhaps  serve  as  a  limit  between  these  two  classes, 
since  it  may  still  be  distinctly  detected  in  aqueous  solu- 
tions by  means  of  the  very  susceptible  reagents  which  we 
possess  for  lime  and  sulphuric  acid. 

When  examining  an  aqueous  fluid  by  evaporating  a 
few  drops  of  it  upon  a  platinum  plate,  there  remains  some- 
times a  very  minute  residue,  which  leaves  us  in  doubt  as 


256  ADDITIONAL   REMARKS. 

to  the  nature  of  the  substance  ;  in  this  case  the  fluid  must, 
1st,  be  tested  with  litmus  papers  ;  2d,  one  drop  of  solu- 
tion of  chloride  of  barium  added  to  a  portion  of  it ;  and, 
lastly,  some  carbonate  of  potash  added  to  another  portion. 
If  these  tests  produce  no  alteration,  it  is  unnecessary  to 
examine  it  further  for  acids  or  bases.  We  may,  in  such 
cases,  feel  certain,  that  the  substance  of  which  the  residue 
remaining  upon  evaporation  consists,  will  be  better  de- 
tected amongst  the  bodies  insoluble  in  water,  since  both 
the  acids  and  bases,  which  principally  form  sparingly  solu- 
ble compounds,  are  sensibly  indicated  by  the  above-men- 
tioned tests. 

If  water  has  dissolved  any  portion  of  the  substance 
under  examination,  the  student  will  always  do  well  to  exa- 
mine separately  this  solution  for  acids  and  bases,  as  this 
will  permit  him  to  detect  the  nature  of  the  compound  under 
examination  with  greater  facility,  and,  moreover,  will  ren- 
der his  conclusions  the  safer,  which  advantages  will  coun- 
terbalance the  disadvantage  of  meeting  sometimes  with 
the  same  substance  in  the  aqueous  and  in  the  acid 
solution. 

The  following  substances  are  insoluble  in  water,  but 
soluble  in  hydrochloric  acid  or  in  nitric  acid,  (with  some 
exceptions,)  the  phosphates,  arseniates,  arsenites,  borates, 
carbonates,  and  oxalates  of  the  earths  and  metals ;  and 
also  several  tartrates,  citrates,  malates,  benzoates,  and  suc- 
cinates,  the  oxides  and  sulphurets  of  the  heavy  metals, 
alumina,  magnesia,  many  metallic  iodides  and  cyanides, 
&c.  Nearly  all  of  these  compounds  are  decomposed,  if 
not  by  dilute,  yet  by  boiling  concentrated  hydrochloric 
acid,  (for  the  exceptions  vide  §  127,)  but  this  decomposi- 
tion gives  rise  to  the  formation  of  insoluble  compounds 
when  oxide  of  silver  is  present,  and  of  sparingly  soluble 
compounds  in  the  presence  of  protoxide  of  mercury  and 
lead.  This  is  not  the  case  with  nitric  acid,  and  thus  we 
often  effect  a  complete  solution  by  its  means  in  cases 
where  hydrochloric  acid  has  left  a  residue.  But  nitric 
acid,  besides  the  substances  insoluble  in  simple  acids, 
leaves  also  oxide  of  antimony,  peroxide  of  tin,  peroxide  of 
lead,  &c.  undissolved,  whilst  it  dissolves  many  other  sub- 
stances more  or  less  completely.  When,  therefore,  the 


DETECTION   OP   THE   BASES.  257 

compound  under  examination  is  not  completely  dissolved 
by  nitric  acid,  (with  the  exception  of  sulphur,  which  may 
have  separated,)  we  must  in  the  course  of  analysis  again 
have  recourse  to  the  hydrochloric  solution,  in  order  to 
assign  exact  limits  in  some  measure  to  the  third  class  of 
substances,  viz.  those  bodies  which  are  insoluble  in  water 
and  simple  acids. 

With  regard  to  the  solution  of  pure  metals  or  alloys,  we 
must  remark,  that  white  precipitates  frequently  are  formed 
upon  boiling  with  nitric  acid,  though  no  tin  or  antimony  be 
present.  Inexperienced  students  often  confound  these 
precipitates  with  the  oxides  of  these  two  metals,  although 
their  external  appearance  is  quite  different.  These  preci 
pitates  consist  of  nitrates  sparingly  soluble  in  the  nitric 
acid  present,  but  of  easy  solution  in  water.  Consequently, 
before  we  can  pronounce  these  precipitates  to  consist  of 
tin  or  antimony,  we  must  previously  ascertain  whether 
they  are  soluble  in  water. 


From  §  107  to  §  129. 

A.  GENERAL  SURVEY  AND  EXPLANATION  OF  THE  ANALYTICAL 
COURSE. 

a.  DETECTION  OF  THE  BASES. 

We  have  divided  the  bases  into  six  groups,  (vide  Chap- 
ter III.  Part  I.)  and  explained  the  method  of  detecting  and 
isolating  the  individual  bases.  These  objects  we  have  kept 
in  view  in  the  practical  course,  and  as  a  correct  apprehen- 
sion of  this  is  of  primary  importance,  we  subjoin  a  brief 
explanation  of  the  grounds  of  our  division, — a  key,  as  it 
were,  to  the  analytical  course  of  study,  so  far  as  those 
bases  are  concerned.  The  general  reagents  which  we 
employ  in  the  course  of  analysis  to  divide  the  bases  into 
principal  groups,  are  HYDROCHLORIC  ACID,  SULPHURETTED 

HYDROGEN,  HYDROSULPHURET  OF  AMMONIA,  and  CARBONATE 

OF  AMMONIA  ;  this  is  also  the  order  of  succession  in  which 
they  are  employed.  Hydrosulphuret  of  ammonia  performs 
a  double  part. 

Let  us  suppose  we  have  in  solution  all  the  bases»  arse- 


258  DETECTION    OP    THE    BASES. 

nious  acid,  and  phosphate  of  lime,  (which  latter  may  serve 
as  a  type  for  the  salts  of  the  alkaline  earths,  soluble  in 
acids,  and  precipitated  by  ammonia,  unaltered.) 

Chlorine  forms  insoluble  compounds  with  silver  and 
mercury  alone ,  chloride  of  lead  is  sparingly  soluble  in 
water.  The  insoluble  protochloride  of  mercury  corres- 
ponds with  the  protoxide  of  mercury.  If,  therefore,  we 
L  dd  to  our  solution 

1 .  Hydrochloric  acid,  we  remove  from  the  solution  the 
metallic  oxides  of  the  first  section  of  the  fifth  group,  viz. 
the  OXIDE  OP  SILVER  and  the  PROTOXIDE  OF  MERCURY.     A 
portion  of  the  LEAD,  also,  may,  perhaps,  precipitate  as  chlo- 
ride of  lead,  should  the  solution  be  concentrated  ;  this  is, 
however,  immaterial,  as  a  sufficient  quantity  of  the  lead 
remains  in  solution  as  to  admit  of  its  detection  afterwards. 

Sulphuretted  hydrogen  precipitates  the  oxides  of  the 
fifth  and  sixth  group  completely  from  solutions  containing 
a  free  mineral  acid,  as  both  the  affinity  which  the  metallic 
radicals  of  these  oxides  have  for  sulphur,  and  that  which 
hydrogen  possesses  for  oxygen,  are  so  powerful  as  to 
overcome  the  affinity  between  the  metal  and  oxygen, 
together  with  that  between  the  oxide  and  a  strong  acid, 

EVEN  THOUGH  THE  ACID  BE  PRESENT  IN  EXCESS.   But 

none  of  the  other  bases  are  precipitated  under  those 
circumstances,  the  bases  of  the  first,  second,  and  third 
group  forming  no  sulphur  compounds  insoluble  in  water  ; 
those  of  the  fourth  group  are  not  precipitated,  because  the 
affinity  which  their  metallic  radicals  possess  for  sulphur, 
together  with  that  manifested  by  hydrogen  for  oxygen,  are 
not  sufficiently  powerful  to  overcome  that  of  the  metal 
for  oxygen,  and  of  the  oxide  for  a  strong  acid,  IF  THE 

LATTER  IS  NOT   PRESENT  IN  EXCESS. 

If,  therefore,  after  the  removal  of  oxide  of  silver  and  of 
p  toxide  of  mercury,  by  means  of  hydrochloric  acid,  we 
add  to  our  solution,  (which  still  contains  free  hydrochloric 
ccid,) 

2,  Sulphuretted  hydrogen  :  we  remove  from  it  the  rest 
of  the  oxides  of  the  fifth,  together  with  those  of  the  sixth 

group,  Viz.  OXIDE  OF  LEAD,  PEROXIDE  OF  MERCURY,  OXIDE 
OF  COPPER,  OXIDE  OF  BISMUTH,  OXIDE  OF  CADMIUM,  PEROX- 
IDE OF  GOLD,  PEROXIDE  OF  PLATINUM,  PROTOXIDE  OF  TIN, 


DETECTION  OF  THE  BASES.  259 

PEROXIDE  OF  TIN,  OXIDE  OF  ANTIMONY,  ARSENIOUS  ACID, 

and  ARSENIC  ACID.  All  the  other  oxides  remain  in  solu- 
tion, either  unaltered  or  reduced  to  a  lower  degree  of  oxi- 
dation, e.  g.  peroxide  of  iron,  chromic  acid,  &c. 

The  sulphurets  corresponding  with  the  oxides  of  the 
sixth  group  have  the  property  of  combining  with  electro- 
positive metallic  sulphurets  (the  sulphurets  of  the  alkali 
metals)  forming  sulphur  salts  soluble  in  water,  whilst  the 
sulphurets  corresponding  with  the  oxides  of  the  fifth  group 
do  not  possess  this  property.  If,  therefore,  we  treat  all 
the  sulphurets  precipitated  by  sulphuretted  hydrogen  from 
acid  solution,  with 

3.  Hydrosulphuret  of  ammonia,  or  sulphur et  of  potas 
sium,  the  bisulphurets  of  mercury,  lead,  copper,  bismuth, 
and  cadmium  will  remain  undissolved,  whilst  the  other 
bisulphurets  are  dissolved  as  the  double  SULPHURETS  OF 
GOLD,  PLATINUM,  ANTIMONY,  TIN,  ARSENIC,  ancl  ammonium 
or  potassium,  and  from  this  solution  they  are  precipitated 
upon  the  addition  of  an  acid,  either  unaltered,  or  having 
acquired  a  higher  degree  of  sulphuration,  by  receiving 
sulphur  from  the  hydrosulphuret  of  ammonia,  (sulphuret 
of  tin.)  In  this  process  the  acid  decomposes  the  sulphur 
salt  formed.  The  sulphur  base  (hydrosulphuret  of  am- 
monia or  sulphuret  of  potassium)  is  decomposed  at  the  ex- 
pense of  the  constituents  of  decomposed  water,  into  an 
oxygen  base  (ammonia  or  potash)  and  sulphuretted  hydro- 
gen ;  the  former  combines  with  the  acid  added,  the  latter 
escapes,  and  the  liberated  electro-negative  sulphur  pre- 
cipitates. (If  the  acid  is  an  hydracid,  its  radical  combines 
with  the  ammonium  and  its  hydrogen  with  the  sulphur.) 
Sulphur  precipitates  at  the  same  time,  the  hydrosulphuret 
of  ammonia  always  containing  sulphur  in  excess.  This 
sulphur  renders  the  colour  of  the  precipitated  sulphurets 
lighter,  which  must  be  always  borne  in  mind,  when  deter- 
mining their  nature. 

Of  the  oxides  still  in  solution,  the  alkalies,  the  alkaline 
earths,  alumina  and  oxide  of  chromium  have  remained  so; 
because  their  sulphur  compounds  are  soluble  in  water,  or 
because  their  salts  are  not  at  all  affected  by  sulphuretted 
hydrogen  ;  the  oxides  of  the  fourth  group  would  have  been 
precipitated  by  sulphuretted  hydrogen,  had  not  the  free 


260  DETECTION    OF   THE    BASES. 

acid  present  prevented  their  precipitation,  as  their  corre- 
sponding sulphur  compounds  are  insoluble  in  water.  If, 
therefore,  this  free  acid  be  removed,  i.  e.  if  the  solution  be 
made  alkaline  and  sulphuretted  hydrogen  added,  or  if,  what 
answers  both  purposes  at  once, 

4.  Hydrosulphuret  of  ammonia  be  added  to  the  solu- 
tion, the  sulphurets  corresponding  with  the  oxides  of  the 
fourth  group  are  precipitated,  viz.  :  SULPHURET  OF  IRON> 

SULPHUKET    OF    MANGANESE,  StJLPHURET    OF    COBALT,  STJL- 

PHURET  OF  NICKEL,  and  si/LPHURET  OF  ZINC,  and  at  the 
same  time,  ALUMINA,  OXIDE  OF  CHROMIUM,  and  PHOSPHATE 
OF  LIME,  are  precipitated,  the  affinity  which  the  ammonia 
possesses  for  the  acid  of  the  salt  of  oxide  of  chromium  or 
of  alumina,  or  for  the  acid  which  keeps  the  phosphate  of 
lime  in  solution,  causing  decomposition  of.  the  water  and 
subsequently  formation  of  oxide  of  ammonium  and  of 
sulphuretted  hydrogen.  The  former  combines  with  the 
acid,  the  latter  escapes,  incapable  of  entering  into  com- 
bination with  the  oxides  deprived  of  their  acids  or  with 
the  phosphate  of  lime, — the  oxides  and  the  limesalt  preci- 
pitate. We  have  now  remaining  in  solution  only  the 
alkaline  earths  and  the  alkalies.  The  neutral  carbonates 
of  the  former  are  insoluble  in  water,  whilst  those  of  the 
latter  are  soluble.  If,  therefore,  we  add 

5.  Carbonate  of  ammonia  and  apply  heat,  in  order  to 
decompose  acid  carbonates  which  may,  peradventure,  have 
been  formed,  all  the  alkaline  earths  ought  to  precipitate. 
This  is,  however,  the  case  only  as  regards  BARYTES, 
STRONTIAN,  and  LIME  \  of  magnesia  we  know  that,  owing 
to  its  disposition  of  forming  double  compounds  with 
ammoniacal  salts,  it  precipitates  only  in  part,  or,  not  at 
all,  in  presence  of  another  ammoniacal  salt.  To  avoid 
this  uncertainty,  sal  ammoniac  is  added  previous  to  the 
addition  of  carbonate  of  ammonia,  in  order  completely  to 
prevent  the  precipitation  of  magnesia. 

We  have  now  still  in  solution,  magnesia  and  the  alkalies  ; 
of  the  presence  of  magnesia  we  may  assure  ourselves  by 
means  of  phosphate  of  soda  and  ammonia  ;  but  for  its 
separation  we  pursue  a  different  way,  since  the  presence 
of  phosphoric  acid  would  impede  the  further  progress  of 
the  analysis.  The  process  which  we  employ  is  based 


DETECTION  OF  THE  ACIDS.  261 

either  upon  magnesia  being  insoluble  in  its  pure  state  or  as  a 
carbonate.  The  substance  under  examination  is  heated  to 
redness  in  order  to  expel  the  ammoniacal  salts,  and  the 
magnesia  is  then  either  precipitated  by  means  of  barytes 
whilst  the  alkalies  remain  in  solution ;  or  the  substance  is 
heated  to  redness,  with  the  addition  of  sulphuric  acid,  and 
the  sulphates  formed  are  by  decomposition  with  acetate  of 
barytes,  converted  into  acetates,  and  these,  by  the  applica- 
tion of  a  red  heat,  into  carbonates  ;  upon  treating  these 
latter  with  water,  carbonate  of  magnesia  remains,  whilst 
the  alkaline  carbonates  are  dissolved.  A  fresh  specimen 
must,  of  course,  be  employed  for  the  detection  of  ammonia. 

b.    DETECTION    OF    THE    ACIDS. 

Previous  to  entering  upon  the  examination  for  acids  and 
electro-negative  substances,  we  must  first  consider  which 
of  these  bodies  may  and  which  of  them  cannot  be  present 
according  to  the  detected  bases,  and  accordingly  to  the 
solubility  of  the  substances  under  examination  ;  thus  we 
shall  avoid  making  unnecessary  experiments.  A  table 
useful  for  this  purpose,  will  be  found  in  the  appendix. 
The  general  reagents  employed  for  the  detection  of  acids 
are,  for  the  inorganic  acids,  CHLORIDE  OF  BARIUM  and 
NITRATE  OF  SILVER  ;  for  the  organic  acids,  CHLORIDE  OF 
CALCIUM  and  PERCHLORIDE  of  IRON.  It  is,  therefore,  in- 
dispensable, first  to  assure  ourselves  whether  we  have 
to  operate  upon  a  substance  containing  inorganic  acids 
alone,  or  organic  acids  alone,  or  both  together.  When 
examining  for  bases,  the  general  reagents  serve  for  the 
real  separation  of  the  various  groups  of  bases  from  each 
other ;  in  the  examination  for  acids,  we  only  use  them  to 
assure  ourselves  of  the  presence  or  absence  of  the  acids 
belonging  to  the  different  groups. 

Let  us  suppose  we  have  in  an  aqueous  solution  all  the 
acids  we  have  treated  of  in  the  present  work,  combined, 
for  instance,  with  soda. 

Barytes  form  insoluble  .compounds  with  sulphuric  acid, 
phosphoric  acid,  arsenious  acid,  arsenic  acid,  carbonic 
acid,  silicic  acid,  boracic  acid,  chromic  acid,  oxalic  acid, 
tartaric  acid,  and  citric  acid  ;  these  compounds  are  soluble 
in  hydrochloric  acid,  with  the  exception  of  sulphate  of 
11* 


262  DETECTION    OF    THE   ACIDS. 

barytes.     If,  therefore,  to  a  portion  of  our  neutral  or  neu- 
tralized solution,  we  add 

1.  Chloride  of  barium,  the  presence  of  at  least  one  of 
these  acids  will  immediately  become  manifest.  Upon 
treating  the  precipitate  formed  with  hydrochloric  acid,  the 
presence  of  sulphuric  acid  will  be  detected,  as  all  the  salts 
of  barytes  are  soluble  in  this  menstruum,  with  the  excep- 
tion of  the  sulphate.  When  sulphate  of  barytes  is  present, 
the  reaction  with  chloride  of  barium  does  not  enable  us  to 
detect  all  the  other  acids  enumerated  with  safety.  For 
upon  filtering  the  hydrochloric  solution  of  the  precipitates 
and  supersaturating  with  ammonia,  the  borate,  tartrate, 
citrate,  &c.  of  barytes  do  not  precipitate  again,  being  kept 
in  solution  by  the  sal  ammoniac  formed.  Chloride  of  ba- 
rium, therefore,  cannot  be  employed  to  separate 'the  indi- 
vidual acids  from  each  other,  and  thus  is  of  no  use  for  their 
individual  detection,  except  for  that  of  sulphuric  acid.  It 
is,  however,  of  great  importance  as  a  reagent,  since  the 
non-formation  of  a  precipitate  in  neutral  or  alkaline  solu- 
tions, upon  its  application  proves  at  once  the  absence  of 
a  considerable  number  of  acids. 

Silver  forms  compounds  insoluble  in  water,  with  chlo- 
rine, iodine,  bromine  and  cyanogen  ;  and  oxide  of  silver, 
with  phosphoric  acid,  arsenious  acid,  arsenic  acid,  boracic 
acid,  chromic  acid,  silicic  acid,  oxalic  acid,  tartaric  acid, 
and  citric  acid.  All  these  compounds  are  soluble  in  am- 
monia, with  the  exception  of  iodide  of  silver,  and  in  nitric 
acid,  with  the  exception  of  iodide,  chloride,  bromide,  and 
cyanide  of  silver.  If,  therefore,  we  add  to  our  solution 
(which  must  be  completely  neutral,) 

2.  Nitrate  of  silver,  we  detect  immediately  the  pre- 
sence of  one  or  several  of  the  acids  enumerated  ;  chromic 
acid,  arsenic  acid,  and  several  other  acids,  the  silver  salts 
of  which  are  coloured,  may  even  be  individually  detected 
with  a  certain  degree  of  safety,  by  the  colour  of  their  pre- 
cipitates. If  we  add  nitric  acid  to  the  precipitate,  we 
detect  the  presence  of  the  haloid  compounds,  as  these 
remain  undissolved,  whilst  the  oxide  salts  are  dissolved. 
The  complete  separation  and  individual  detection  of  those 
acids  which  form  insoluble  compounds  with  oxides  of 
silver,  are  prevented  by  the  same  cause  which  renders  the 


DETECTION    OP    THE    ACIDS.  263 

individual  detection  of  acids  by  chloride  of  barium  unsafe. 
For  the  arnmoniacal  salt  formed  prevents  the  reprecipita- 
tion  by  ammonia,  of  several  salts  of  silver,  from  the  acid 
solution ;  nitrate  of  silver  serves  us,  therefore,  besides  de- 
tecting chlorine,  iodine,  bromine,  and  cyanogen,  and  indi- 
cating chromic  acid,  &c.,  especially  to  prove  at  once  the 
absence  of  many  acids,  if  it  produces  no  precipitate  in  neu- 
tral solutions.  The  behaviour  of  solutions  under  exami- 
nation with  chloride  .of  barium  and  with  nitrate  of  silver, 
therefore,  points  out  at  once  what  course  we  have  further 
to  pursue  in  our  investigation.  Thus,  for  instance,  if 
chloride  of  barium  has  produced  a  precipitate,  whilst  we 
have  obtained  none  by  nitrate  of  silver,  it  is  not  necessary 
to  test  for  phosphoric  acid,  chromic  acid,  boracic  acid, 
silicic  acid,  arsenious  acid,  arsenic  acid,  oxalic  acid,  tarta- 
ric  acid,  and  citric  acid,  provided  always  that  the  solution 
does  not  already  contain  ammoniacal  salts.  The  same  is 
the  case  if  we  obtain  a  precipitate  by  nitrate  of  silver,  but 
none  by  chloride  of  barium.  Returning  to  our  first  sup- 
position, viz.,  that  all  acids  are  present  in  the  compound 
under  examination,  we  have  thus  detected  CHLORINE, 
BROMINE,  IODINE,  and  CYANOGEN,  (for  their  separation  and 
individual  detection,  vide  §  100,)  as  well  as  SULPHURIC  " 
ACID,  and  we  have  reason  further  to  test  for  all  the  other 
acids  precipitated  by  these  two  reagents.  Their  detection 
is  based  upon  the  results  of  special  experiments,  which 
have  already  been  explained  in  the  course  of  the  present 
work :  the  same  applies  to  the  other  inorganic  acids,  and 
thus  also  to  nitric  acid  and  chloric  acid. 

Of  the  organic  acids,  oxalic  acid,  tartaric  acid,  and 
paratartaric  acid,  are  precipitated  by  chloride  of  calcium, 
from  aqueous  solutions,  at  a  low  temperature,  even  in  the 
presence  of  sal  ammoniac  ;  but  the  precipitation  of  citrate 
of  lime  is  prevented  by  the  presence  of  ammoniacal  salts, 
and  takes  place  only  upon  boiling  or  upon  mixing  the  so- 
lution with  alcohol ;  the  latter  means  is  also  employed  for 
the  separation  of  oxalic  lime  from  aqueous  solutions.  If, 
therefore,  we  add  to  our  solution, 

3.  Chloride  of  calcium  and  sal  ammoniac,  OXALIC  ACID, 
TARTARIC  ACID,  and  PARATARTARIC  ACID  are  precipitated, 
but  the  lime-salts  of  several  inorganic  acids,  which  have 
not  yet  been  separated,  precipitate  at  the  same  time  (phos- 


264  SPECIAL    REMARKS. 

phate  of  lime,  for  instance.)  We  must,  therefore,  select, 
for  the  individual  detection  of  the  precipitated  organic 
acids,  such  reactions  only  as  do  not  admit  the  possibility 
of  confounding  the  organic  acids  with  the  inorganic  acids 
precipitated  at  the  same  time.  For  the  detection  of  oxalic 
acid  we  thus  select  solution  of  gypsum,  with  the  addition 
of  acetic  acid,  (§  98,  c,  4,)  for  the  detection  of  tartaric  and 
paratartaric  acid ;  we  treat  the  precipitate  produced  by 
chloride  of  calcium,  with  solution  of  potash,  since  the  lime- 
salts  of  these  two  acids  alone  dissolve  in  this  menstruum,  at 
a  low  temperature,  whilst  all  the  other  insoluble  lime- salts 
remain  undissolved. 

Of  the  organic  acids  we  have  now  still  in  solution  citric 
acid  and  malic  acid,  succinic  acid  and  benzoic  acid,  acetic 
acid  and  formic  acid.  CITRIC  ACID  and  MALIC  ACID  pre- 
cipitate upon  alcohol  being  added  to  the  fluid  filtered  off 
from  the  oxalate,  tartrate,  &c.,  of  lime,  and  which  contains 
still  chloride  of  calcium  in  excess.  Sulphate  and  borate 
of  lime  always  precipitate  together  with  the  malate  and 
citrate  of  lime,  if  sulphuric  acid  and  boracic  acid  are  pre- 
sent ;  we  must,  therefore,  carefully  guard  against  con- 
founding the  lime  precipitates  of  these  acids  with  those  of 
citric  acid  and  malic  acid.  The  alcohol  is  then  removed 
by  evaporation,  and 

4.  Perchloride  of  iron  added  ;  this  precipitates  SUC- 
CINIC ACID  and  BENZOIC  ACID  in  combination  with  pe- 
roxide of  iron,  whilst  FORMIC  ACID  and  ACETIC  ACID  re- 
main in  solution.  The  methods  for.  the  further  separation 
of  the  groups  and  the  reactions  whereupon  the  detection 
of  the  individual  acids  depends,  have  already  been  de- 
scribed. 

B.     SPECIAL  AND  ADDITIONAL  REMARKS  UPON  THE 

SYSTEMATIC    COURSE    OF   ANALYSIS. 

§  114. 

We  have  at  the  beginning  of  §  114,  given  the  instruc- 
tion to  mix  neutral  or  acid  aqueous  solutions  with  hydro- 
chloric acid.  This  acid  must  be  added  drop  by  drop.  If 
no  precipitate  is  formed,  a  few  drops  are  sufficient ;  if  a 
precipitate  is  formed,  the  acid  must  be  added  until  the  pre- 


ADDITIONAL    REMARKS.  265 

cipitate  ceases  to  increase  and  the  fluid  has  acquired  a  dis- 
tinct acid  reaction.     The  addition  of  a  large  proportion  of 
hydrochloric  acid  is  not  only  unnecessary,  but  injurious. 
The  precipitate  produced  by  hydrochloric  acid  in  neutral 
or  acid  solutions  may  consist  of  chloride   of  silver,  proto- 
chloride  of  mercury,  chloride  of  lead,  and  a  basic  salt  of 
antimony.     The    two   latter  substances    redissolve  upon 
diluting  and  heating  the  acid  fluid,  and  thus  the  non-solu- 
tion of  the  precipitate  upon  the  application  of  these  pro- 
cesses, is  an  indication  of  the  probable  presence  of  chloride 
of  silver  or  protochloride  of  mercury.     Should  compounds 
of  antimony  or  bismuth  be  present,  this  dilution  with  water 
will  separate  from  them  insoluble  basic  salts  in  a  state  of 
most  minute  division  ;  these  must  be  redissolved  by  the 
addition  of  hydrochloric  acid,  before  we  can  draw  any  cor- 
rect conclusion  from  the  remaining  or  disappearing  of  the 
precipitate  produced  by  hydrochloric  acid.     If  we  have  to 
operate  upon  an   alkaline  solution,  the  hydrochloric  acid 
must  be  added,  until  the  fluid  manifests  a  strong  acid  re- 
action.    A  great  excess  of  the   acid  must,    however,  be 
avoided.     The  subsiance  which  causes  the  alkaline  reac- 
tion of  the  fluid,  is  neutralized  by  the  hydrochloric  acid, 
and  the  bodies  combined   with   it?  or  dissolved  in    it,  se- 
parate.    If  the  alkali  present  was  in  a  free  state,  oxide  of 
zinc,  for  instance,  alumina,  &c.,  may  be  precipitated.    But 
these  redissolve  in   an  excess   of  the  hydrochloric  acid, 
whilst  chloride  of  silver,  if  present,  will  not  redissolve,  and 
chloride  of  lead  only  sparingly.     If  a  metallic  sulphur  salt 
be  the  cause  of  the  alkaline  reaction,  the  electro-negative 
sulphuret  (e.  g.  sulphuret  of  antimony)  will  precipitate,  on 
the  addition  of  the  hydrochloric  acid ;  whilst  the  electro- 
positive sulphuret,  (e.  g.  sulphuret  of  sodium)  will  form 
chloride  of  sodium,  and  sulphuretted  hydrogen,  with  the 
constituents  of  hydrochloric  acid.  If  an  alkaline  carbonate, 
or  an  alkaline  sulphuret,  be  the  cause  of  the  alkaline  reac- 
tion, carbonic  acid  or  sulphuretted  hydrogen  will  escape. 
All  these  phenomena  ought  to   be  carefully  observed,  for 
they. not  merely  point  out  the  presence  of  the  relative  sub- 
stance, but  also  exclude  entire  series  of  substances  from 
the  further  examination. 


266  ADDITIONAL    REMARKS. 

§   115. 

We  have  already  had  occasion  to  remark,  that  upon  add- 
ing a  reagent  (e.  g.  sulphuretted  hydrogen)  to  a  fluid  un- 
der examination,  a  precipitate  may  or  may  not  ensue.  If 
a  precipitate  is  formed,  this  may  be,  a,  white,  b,  yellow,  c, 
orange,  cZ,  brown  or  black.  Every  one  of  these  various 
cases  is  a  different  answer  given  to  the  question  put  by 
means  of  the  reagent,  and  every  answer  has  a  different 
meaning.  An  accurate  distinction  of  the  individual  case  is, 
therefore,  indispensable.  Any  error  here  must  prevent  the 
student  from  obtaining  correct  results* 

The  colour  of  the  precipitate  is  almost  invariably  point- 
ed out  as  a  criterion  in  the  systematic  course  of  analysis. 
We  may  presume  that  a  darker  precipitate  will  sometimes 
conceal  one  of  a  lighter  colour,  and  thus,  e.  g.  that  yellow 
sulphuret  of  arsenic  may  be  present,  invisible  in  a  preci- 
pitate of  black  sulphuret  of  mercury;  and  so  we  may  al- 
so conclude  that  no  dark  precipitate  can  be  contained  in 
a  light-coloured  one,  e.  g.  no  black  precipitate  in  a  white* 
These  conclusions  cannot,  however,  always  be  drawn  with 
the  same  degree  of  safety,  all  colours  not  contrasting  so 
pointedly  with  each  other  as  black  and  white  ;  but  many 
of  them  rather  merging  into  each  other,  e.  g.  yellow  and 
orange.  Whenever  the  colour  of  the  precipitate  admits 
of  any  doubt  as  to  its  nature,  it  is  always  advisable  to  pur- 
sue that  course  which  the  darker  of  the  colours  in  question 
indicates,  since  in  this  regard  has  been  had  to  all  the  me- 
tals which  can  possibly  have  precipitated,  whilst  in  the 
other  the  metallic  precipitates  of  darker  colour  are  disre- 
garded. The  safer  way  is  always  to  be  preferred,  although 
it  may  be  the  more  protracted. 

A  judicious  distribution  and  economy  of  time  is  especial- 
ly to  be  studied  in  the  practice  of  analysis  ;  many  of  the 
operations  may  be  carried  on  simultaneously,  which  the 
student  will  readily  perceive  and  arrange  for  himself. 

In  such  cases,  where  we  have  before  us  only  metallic 
oxides  of  the  sixth  group,  (e.  g.  oxide  of  antimony,)  and  ox- 
ides of  the  fourth  group,  (e-  g.  the  oxides  of  iron,)  it  is  not 
necessary  for  their  separation  to  precipitate  them  from 
acidified  solutions  by  means  of  sulphuretted  hydrogen,  but 
we  may  at  once  add  hydrosulphuret  of  ammonia  in  excess 


ADDITIONAL    REMARKS.  26? 

to  the  neutralized  solution.  The  sulphuret  of  iron,  &c., 
will  then-  be  obtained  in  a  precipitate,  whilst  the  antimony, 
&c.,  will  remain  in  solution,  from  which,  upon  the  addi- 
tion of  an  acid,  it  will  immediately  precipitate  a  sulphuret 
of  antimony.  This  method  has  the  advantage  of  rendering 
the  fluid  less  dilute  than  when  sulphuretted  hydrogen  is 
employed,  and  moreover  of  facilitating  and  accelerating  the 
operation. 

§  116. 

When  digesting  the  precipitates  produced  by  sulphuret- 
ted hydrogen  from  acid  solutions,  with  hydrosulphuret  of 
ammonia,  it  is  indispensable  to  apply  this  latter  reagent 
in  a  correct  proportion.  A  small  quantity  is  generally 
sufficient,  but  if  sulphuret  of  tin  be  present,  a  somewhat 
larger  amount  must  be  employed.  Inexperienced  students, 
however,  use  so  much  of  it,  that,  upon  the  addition  of  an 
acid,  sulphur  precipitates  to  such  an  amount  that  the  colour 
of  the  metallic  sulphuret,  which  precipitates  at  the  same 
time,  is  quite  obscured  and  concealed  by  it.  The  separa- 
tion and  individual  detection  of  oxide  of  antimony,  peroxide 
of  tin,  and  arsenic,  is  not  very  easy  if  all  three  oxides  have 
been  precipitated  as  sulphurets.  Inexperienced  students 
will  find  it  difficult  safely  to  detect  and  separate  them  be- 
fore the  blow-pipe.  Of  the  many  methods  applicable  for 
the  distinction  of  these  three  metals,  that  given  at  §116 
has  been  proved  the  safest  by  experience.  If  sulphuret  of 
arsenic,  sulphuret  of  antimony,  and  sulphuret  of  tin,  are 
deflagrated  with  nitre  in  excess,  and  carbonate  of  soda,  the 
metals  and  the  sulphur  oxidize  at  the  expense  of  the  oxygen 
of  the  nitric  acid :  we  have,  therefore,  in  the  fused  mass 
alkaline  arseniate,  antimoniate,  sulphate,  and  stannate,  be- 
sides excess  of  nitre  and  carbonate  of  soda.  On  treating 
with  water,  the  alkaline  sulphate  and  arseniate  are  dissolv- 
ed; the  alkaline  antimoniate  is  decomposed  ;  an  insoluble 
acid  salt  remains,  whilst  a  small  amount  of  antimonic  acid 
is  dissolved  in  the  form  of  a  basic  salt.  A  portion  of  the 
peroxide  of  tin  also  dissolves  in  the  carbonated  alkali  pre- 
sent. If  boiling  water  is  employed,  the  amount  of  the 
dissolved  antimonic  acid  and  peroxide'  of  tin  is  not  inconsi- 
derable, whilst  it  is  but  minute  in  cold  water  ;  the  latter  is, 
therefore,  preferable  to  boiling  water  in  this  operation.  If 


268  ADDITIONAL   REMARKS. 

the  alkaline  solution  obtained  is  then  saturated  with  nitric 
acid,  and  heat  applied,  the  dissolved  peroxide  of  tin  and 
antimonic  acid  precipitate  ;  but  this  precipitate  is  never 
free  from  arsenic.  This  will  show  how  caiefully  we  ought 
to  avoid  getting  much  peroxide  of  tin  or  antimonic  acid  in 
solution.  In  the  fluid  saturated  with  nitric  acid,  or  slightly 
acidified,  filtered  off  from  the  precipitate  formed,  we  have 
now  still  arseniated  and  sulphated  alkali.  One  portion  of 
this  fluid  is  tested,  as  stated  §  116;  with  solution  of  silver  and 
ammonia,  and  another  portion  with  solution  of  lead.  Since 
the  fluid  must  be  perfectly  neutral  to  render  the  arseniate  of 
silver  visible,  and  since  it  is  not  always  easy  to  hit  upon 
the  exact  neutralization  point,  the  fluid,  after  the  addition  of 
the  solution  of  silver,  is  covered  with  a  layer  of  dilute  am- 
monia. This  is  the  easiest  method  of  producing  a  precip- 
itate when  but  small  quantities  of  arsenic  are  present.  On 
the  precipitation  with  solution  of  acetate  of  lead,  we  obtain 
a  mixture  of  sulphate  and  arseniate  of  oxide  of  lead.  The 
presence  of  the  sulphate  of  lead  renders  the  quantity  of  the 
precipitate  greater,  and  thus  its  collection  and  testing  before 
the  blow-pipe  more  easy  *,  it,  moreover,  increases  the  bulk 
of  the  button  obtained.  Though  by  means  of  these  reac- 
tions the  presence  of  arsenic  may  be  proved  beyond  doubt, 
yet  the  production  of  metallic  crusts  is  the  safest  test. 

If  the  residue  remaining  upon  treating  the  deflagrated 
mass  with  water,  and  which  is  to  be  examined  for  tin  and 
antimony,  be  not  carefully  washed,  and  thus  freed  from  all 
the  nitre  still  adhering  to  it,  previous  to  fusing  with  cyan- 
ide of  potassium,  explosions  will  take  place,  (§  101,  a,  3,) 
whereby  not  only  the  test  specimens  are  thrown  off,  but  the 
operator  himself  may  meet  with  some  injury. 

§  117. 

If  the  sulphurets  of  the  second  section  of  the  fifth  group 
are  heated  to  the  boiling  point  with  nitric  acid,  lead,  bismuth, 
copper,  and  cadmium,  oxidize  at  the  expense  of  a  portion 
of  the  nitric  acid,  which  decomposes  into  nitric  oxide  and 
oxygen,  the  sulphur  separates,  and  the  oxides  formed  com- 
bine with  another  portion  of  the  nitric  acid,  forming  soluble 
nitrates.  Sulphuret  of  mercury  is  not  decomposed  by 


ADDITIONAL   REMARKS.  269 

nitric  acid,  provided  no  chloride  be  present  at  the  same 
time,  owing  to  imperfect  rinsing.  Ammonia  decomposes 
all  the  metallic  nitrate  dissolved.  But  the  oxides  of  lead 
and  bismuth  are  insoluble  in  an  excess  of  ammonia,  whilst 
those  of  cadmium  and  copper  are  dissolved  by  this  reagent. 
Ammonia, therefore,  affords  us  a  means  of  testing  the  solu- 
tion for  the  presence  of  the  oxides  of  lead  and  bismuth,  as 
well  as  of  precipitating  and  separating  them  from  it.  The 
presence  of  oxide  of  copper  is  also  detected  by  this  rea- 
gent ;  the  ammonia-nitrate  of  copper,  which  is  formed  upon 
its  addition  to  the  fluid  under  examination,  imparting  a 
blue  colour  to  the  fluid.  The  causes  whereupon  the  fur- 
ther separation  and  detection  of  the  four  metals  in  question 
depends,  have  already  been  sufficiently  explained  at  §  91, 
(recapitulation  and  remarks.)  With  regard  to  the  detec- 
tion of  bismuth,  it  must  be  remarked,  that  it  never  suc- 
ceeds if  the  excess  of  acid  present  is  not  as  slight  as 
possible  ;  this  is  best  attained  in  the  manner  described  § 
117.  But  if  the  operator  evaporates  only  nearly  to  dryness, 
so  much  acid  frequently  remains  present,  that  the  separa- 
tion of  a  basic  salt  cannot  be  accomplished. 

Besides  the  method  given  at  §  91,  (recapitulation  and 
remarks,)  and  at  §  117,  for  the  distinction  of  cadmium, 
copper,  lead,  and  bismuth,  the  following  method  also 
leads  with  great  safety  to  the  desired  end.  Carbonate  of 
potash  is  added  to  the  nitric  solution  as  long  as  any  preci- 
pitation takes  place  ;  solution  of  cyanide  of  potassium  in 
excess  is  then  added,  and  heat  applied.  Lead  and  bis- 
muth are  hereby  completely  separated  as  carbonates,  whilst 
copper  and  cadmium  are  obtained  in  solution  as  the  double 
cyanides  of  copper  and  potassium,  and  cadmium  and  pot- 
assium. Lead  and  bismuth  may  then  easily  be  separated 
by  means  of  sulphuric  acid  ;  copper  and  cadmium,  by 
adding  to  the  solution  of  their  cyanides  in  cyanide  of  pot- 
assium) sulphuretted  hydrogen  in  excess,  and  applying 
heat ;  some  more  cyanide  of  potassium  must  then  be 
added  to  redissolve  the  sulphuret  of  copper,  which,  perad- 
venture,  may  also  have  precipitated.  A  yellow  precipitate 
of  sulphuret  of  cadmium,  insoluble  in  cyanide  of  potas- 
sium, indicates  cadmium.  The  fluid  is  filtered  off,  and 
hydrochloric  acid  added  to  the  nitrate  ;  the  formation  of  a 


270  ADDITIONAL   REMARKS. 

black  precipitate  of  sulphuret  of  copper  indicates  copper. 
The  presence  of  mercury  is  indeed  already  proved  by  a 
black  residue  remaining,  upon  heating  the  sulphurets  with 
nitric  acid.     A  more  minute  examination  of  any  residue 
remaining  upon  boiling  with  nitric  acid,  is,  however,  neces- 
sary, always  provided  this   residue  be  not   pure   yellow 
sulphur,  which  in  most  cases  floats  on  the  surface  of  the 
fluid.     The  reasons   for  this   further  examination  are  the 
following  :  separated  sulphur  frequently    envelops   small 
particles  of  the  other  black  sulphurets,  and  for  this  reason 
appears  black   here    and  there.     Sulphuret  of  mercury, 
moreover,  may,  under  certain  circumstances,  lose  its  black 
colour,  and  the  precipitate  in  that  case  be  confounded  with 
sulphate  of  lead,  (into  which  substance  a  portion  of  the 
sulphuret  of  lead  present  is  in  most  cases  converted,)  or 
with  pertoxide  of  tin,  (which  may  have  been  formed  by 
the  action  of  nitric  acid  upon  sulphuret  of  tin  present,  and 
not  completely  removed  by  hydrosulphuret  of  ammonia. 
The  test  with  polished  copper  is  the  most  convenient,  and 
yields  the  quickest  result.     It  must,  however,  be  remarked, 
that  errors   occur  more  frequently,  when  employing  this 
test,  than  when  we  select  the  reaction  with  protochloride 
of  tin.     When   employing  the   latter   reagent,   we   must 
especially  assure  ourselves  of  its  being  still  undecomposed, 
and  of  the  solution  of  mercury  containing  no   nitric  acid. 
If  after  the    method  described,   the  protoxide  of  mercury 
has  first  been  separated  by  hydrochloric  acid,  and  a  preci- 
pitate of  sulphuret  of  mercury  is  formed,  upon  the  addition 
of  sulphuretted  hydrogen,  this    corresponds   always    with 
the  peroxide  and  perchloride,  &c.  of  mercury.     If  we  have 
to  operate  upon  an  aqueous  solution,  or  a  solution  in  very 
dilute  hydrochloric  acid,  it  existed  as   such  in  the  original 
substance.     But  when  we  have  a  nitric  solution  before  us, 
it  may  have  originally  existed  as   protoxide,  and   subse- 
quently acquired  a  higher  degree  of  oxidation. 

§  118. 

The  precipitate  produced  by  hydrosulphuret  of  ammo- 
nia, may  (as  we  have  already  stated,  page  259)  consist  of 
sulphurets,  of  oxides,  and  of  the  phosphates  of  the  alkaline 


ADDITIONAL  REMARKS.  271 

earths,  phosphate  of  alumina,  oxalate  of  lime  (barytes  and 
strontian.)  The  borates  of  the  alkaline  earths  and  the 
oxalate  of  magnesia  would,  moreover,  be  precipitated,  but 
they  remain  in  solution,  owing  to  the  sal  ammoniac  formed 
in  the  fluid  or  added  to  it.  Upon  dissolving  the  precipitate 
in  hydrochloric  acid,  or  in  aqua  regia,  the  metallic  sul- 
phurets  and  the  hydrated  oxides  are  converted  into  soluble 
chlorides,  whilst  the  phosphates  and  oxalates  dissolve 
without  decomposition.  If  to  this  acid  solution,  ammonia 
is  added,  the  phosphates  and  oxalates  are  re-precipitated, 
and,  together  with  them,  alumina,  oxide  of  chromium,  and 
peroxide  of  iron  fall  down,  as  these  do  not  (like  the  oxides 
of  manganese,  nickel,  cobalt,  and  zinc)  form  soluble  double 
compounds  with  ammoniacal  salts.  This  precipitation  by 
ammonia,  in  presence  of  sal  ammoniac,  is  the  base  where- 
on the  further  distinction  and  individual  detection  of  the 
substances  enumerated  depends.  At  this  result  we  may 
also  arrive  by  merely  adding  sal  ammoniac  and  ammonia  in 
excess  to  the  fluid  filtered  from  the  precipitate  produced 
by  sulphuretted  hydrogen,  after  having  expelled  the  excess 
of  sulphuretted  hydrogen  by  boiling,  and  converted  the 
iron  which,  peradventure,  may  be  present,  into  peroxide 
of  iron,  by  heating  with  nitric  acid.  We  obtain  thus,  of 
course,  the  peroxide  of  iron,  the  alumina,  oxide  of  chro- 
mium, and  the  phosphates,  &c.,  of  the  alkaline  earths 
alone  in  the  precipitate,  whilst  the  manganese,  cobalt, 
nickel,  and  zinc,  are  contained  in  the  fluid  which  runs  off, 
and  may  then  be  precipitated  by  means  of  hydrosulphuret 
of  ammonia.  Under  certain  circumstances  this  method  is 
preferable  to  the  first,  and  may  then  be  employed  with 
advantage  ;  but  in  general  it  requires  more  time  than  the 
other.  With  regard  to  the  further  detection  of  nickel, 
cobalt,  manganese,  and  zinc,  we  have  nothing  to  add  to 
§  1 18,  2,  except  that  ammoniacal  salts  must  not  be  present, 
if  the  separation  of  these  four  metals  from  each  other  is  to 
succeed  after  the  method  described  at  §  118,  2.  But  as 
the  separation  of  manganese,  nickel,  &c.,  from  iron,  &c., 
depends  upon  the  presence  of  ammoniacal  salts,  these  must 
be  removed  either  by  evaporating  the  solution  and  heating 
th  residue  to  redness,  or  by  precipitating  these  four  me- 
tals again  by  hydrosulphuret  of  ammonia,  (which  latter 


272  ADDITIONAL    REMARKS. 

method  generally  is  preferable  to  the  former.)  The  pre- 
cipitate of  the  metallic  sulphurets  must,  of  course,  be 
carefully  washed.  The  separation  of  the  peroxide  of  iron, 
and  of  the  phosphates  and  oxalates  of  the  alkaline  earths 
from  alumina  and  oxide  of  chromium  rests  upon  the  solu- 
bility of  the  latter  and  the  insolubility  of  the  former  com- 
pounds, in  caustic  potash  ;  and  that  of  peroxide  of  iron 
from  the  salts  of  the  alkaline  earths,  upon  the  circumstance 
that  the  precipitation  of  the  former  is  prevented  by  adding 
tartaric  acid  to  the  acid  solution,  previous  to  the  addition 
of  ammonia,  which  is  not  the  case  with  the  latter.  (Vide 
recap,  and  rem.  to  §  88.) 

§  127. 

The  third  class  of  substances  also  has  no  strictly  defina- 
ble limits,  as  the  solubility  or  insolubility  of  several  com- 
pounds belonging  to  it,  depends  very  much  upon  the 
quantity  and  concentration  of  the  acid  and  the  time  of 
boiling.  Besides  the  difficultly  soluble  substances  enu- 
merated, we  must  especially  look  for  many  metallic  sul- 
phurets and  iodides,  which  also  only  dissolve  after  some 
time  in  concentrated  hydrochloric  acid,  at  a  high  tempera- 
ture. If  a  substance  is  dissolved  in  nitric  acid  after  long 
boiling,  we  must  not  conclude  that  protochloride  of  mercury 
is  absent,  since  this  substance,  as  we  have  already  stated, 
is  converted  in  this  process  into  pernitrate  of  mercury  and 
perchloride  of  mercury,  and  is  thus  dissolved. 

Chloride  of  silver,  protochloride  of  mercury,  and  chlo- 
ride of  lead  may  have  been  present  in  the  original  com- 
pound as  such,  or  may  have  been  formed  upon  treating 
with  hydrochloric  acid.  The"  presence  of  chloride  of  lead 
has  in  that  case  already  been  detected  in  the  aqueous  solu- 
tion ;  of  the  original  presence  of  the  two  other  substances 
we  may  assure  ourselves  in  the  following  manner.  The 
substance  insoluble  in  water  is  treated  with  dilute  nitric 
acid.  All  the  salts  of  protoxide  of  mercury  and  oxide  of 
silver  present  are  thereby  dissolved,  whilst  the  chlorides 
enumerated  above  remain  undissolved  together  with  iodide 
of  silver  ;  they  are  separated  by  means  of  ammonia,  which 
at  the  same  time  allows  us  to  detect  the  protochloride  of 
mercury. 


ADDITIONAL  REMARKS.  273 

The  decomposition  of  the  sulphates  of  the  alkaline  earths 
may  be  effected  also  in  the  humid  way  by  boiling  them 
for  some  time  with  solution  of  carbonate  of  potash.  But 
the  fusion  with  the  carbonate  of  potash  and  soda,  yields 
far  safer  results,  and  leads  quickly  to  the  desired  end,  when 
operating  upon  small  quantities.  This  method  has,  more- 
over, the  advantage  of  leading  to  the  safe  detection  of  the 
presence  of  silicic  acid. 

The  sulphates  of  the  alkaline  earths  are  decomposed  by 
the  alkaline  carbonates  in  such  a  manner  as  to  give  rise  to 
the  formation  of  carbonates  of  the  alkaline  earths  and  of 
sulphates  of  the  alkalies.  If  the  precipitate  of  the  former 
be  not  carefully  washed,  previously  to  its  solution  in  hy- 
drochloric acid,  sulphates  of  the  alkaline  earths  will  again 
be  formed  by  the  action  of  the  sulphated  alkali  still  adher- 
ing to  the  precipitate  ;  this  would  render  the  experiment 
very  unsafe  at  the  least,  since,  for  instance,  all  the  barytes 
dissolved  might  precipitate  again. 

Carbon  has  been  connected  with  this  third  class,  since 
it  occurs  sometimes  in  the  course  of  examinations,  and  thus 
may  become  a  great  obstacle  to  the  progress  of  the  inex- 
perienced student,  if  not  prepared  for  its  presence.  Gra- 
phites is  distinguished  from  the  other  forms  of  carbon  by 
its  difficult  combustion  before  the  blow-pipe,  and  its  non- 
combustion  in  a  platinum  spoon  ;  besides  the  iron,  which 
it  generally  contains  in  admixture,  indicates  its  presence. 

§128. 

The  analysis  of  cyanogen  compounds  is  not  very  easy 
in  certain  cases,  and  sometimes  it  is  indeed  extremely  diffi- 
cult to  ascertain  whether  we  have  a  cyanide  before  us  or 
not*  If,  however,  the  phenomena  which  the  substance  un- 
der examination  manifests,  when  heated  to  redness  (§  105, 
A,  I.,  2,  /,)  be  carefully  observed,  and  also  whether  upon 
boiling  with  hydrochloric  acid  any  odour  of  hydrocyanic 
acid  manifests  itself,  (§  106,  A,  2,)  the  presence  or  ab- 
sence of  a  cyanide  will  generally  not  long  be  doubtful. 

It  must  above  all  be  borne  in  mind  that  the  insoluble 
cyanogen  compounds  occurring  in  pharmacy,  &c.,  belong 
to  two  quite  different  classes.  They  are  either  SIMPLE  CY- 


274  ADDITIONAL   REMARKS. 

ANIDES,  or  compounds  of  metals  with  ferrocyanogen,  or 
with  some  other  similar  compound  radical. 

All  the  simple  cyanides  are  decomposed  by  boiling  with 
concentrated  hydrochloric  acid,  into  metallic  chlorides  and 
hydrocyanic  acid.  Their  analysis,  therefore,  is  never  diffi- 
cult. The  ferrocyanides,  &c.,  however,  (to  which  the 
method  given  §  128  indeed  exclusively  refers,)  undergo 
by  acids  such  complicated  decompositions  that  their  analy- 
sis in  this  manner  does  not  easily  succeed.  Their  decom- 
position by  alkalies  is  far  more  simple  ;  these  precipitate 
the  metal  combined  with  the  ferrocyanide,  &c.,  as  oxide, 
by  yielding  their  oxygen  to  it,  and  combining  in  their  me- 
tallic state  with  the  compound  radicals,  forming  soluble 
ferrocyanide  of  potassium,  &c.  The  method  given  at  § 
128  endeavours  first  to  effect  a  decomposition  of  this  kind 
by  means  of  CARBONATE  OF  POTASH.  If  this  succeeds,  we 
have  the  advantage  of  obtaining  the  oxides  as  a  precipitate, 
which  circumstance  renders  their  further  analysis  simple  ; 
if  it  does  not  succeed,  we  must  "have  recourse  to  CAUSTIC 
POTASH.  But  in  an  excess  of  caustic  potash,  several  ox- 
ides are  soluble,  such  as  oxide  of  lead,  oxide  of  zinc,  &c. 
If,  therefore,  e.  g.  the  double  ferrocyanide  of  zinc  and  po- 
tassium, be  boiled  with  caustic  potash,  it  will  completely 
dissolve  in  that  menstruum.  Were  we -to  add  an  acid  to 
this  solution,  we  should  re-obtain  our  original  precipitate 
of  the  double  ferrocyanide  of  zinc  and  potassium,  and  our 
experiment  thus  would  be  of  no  avail.  To  prevent  this, 
we  transmit  sulphuretted  hydrogen  through  the  solution. 
All  the  heavy  metals  dissolved  as  oxides  in  the  potash  so- 
lution are  thereby  converted  into  sulphurets.  Those  of 
them  which  are  insoluble  in  potash,  such  as  sulphuret  of 
lead,  sulphuret  of  zinc,  &c.,  precipitate,  whilst  those  solu- 
ble in  alkaline  sulphurets,  such  as  sulphuret  of  tin,  sulphu- 
ret of  antimony,  &c.,  remain  in  solution,  and  precipitate 
only  upon  the  addition  of  an  acid. 

The  cyanogen  is  always  contained  in  the  liquid  filtered 
from  the  precipitated  oxides  or  sulphurets,  as  ferrocyanide, 
&c.,  of  potassium,  (provided  always  the  compound  before 
us  has  a  double  compound  of  cyanogen  radicals.)  From 
most  of  them  (ferrocyanide,  ferricyanide,  chromicyanide, 
and  manganocyanide  of -potassium)  the  cyanogen  partly 


ADDITIONAL  REMARKS.  275 

• 

separates  as  hydrocyanic  acid,  upon  boiling  this  solution 
with  sulphuric  acid,  and  may  thus  be  easily  detected.  But 
the  cobalticyanide  of  potassium  is  not  decomposed  by 
sulphuric  acid,  and  this  renders  it  difficult  DIRECTLY  to 
prove  the  presence  of  cyanogen  in  this  double  compound. 
Upon  fusion  with  nitre,  all  these  double  compounds  are 
decomposed,  cobalticyanide  of  potassium  not  excepted. 
They  must  previous  to  this  operation  be  treated  with  an 
excess  of  nitric  acid,  and  then  concentrated  by  evaporation, 
or  else  explosions  will  ensue.  Caution  in  this  operation  is 
highly  advisable.  If  we  merely  propose  to  detect  the 
bases  present  in  simple  or  double  cyanides,  it  is  in  most 
cases  sufficient  either  to  heat  the  substance  to  redness  for 
some  time  by  itself,  or  better  still,  to  fuse  it  together  with 
the  carbonates  of  potash  and  soda.  By  this  process  the 
metals  are  obtained  either  in  their  metallic  state,  or  com- 
bined with  carbon.  If  the  compound  has  been  fused 
together  with  the  carbonated  alkalies,  we  obtain  in  the 
dross,  cyanate  of  potassium,  if  this  substance  has  not  been 
converted  into  cyanate  of  potash,  owing  to  the  adventitious 
presence  of  reducible  oxides.  (Vide  §  100,  d,  1.) 


APPENDIX  TO  PART  SECOND. 


L 


GENERAL  SCHEME  FOR  A  JUDICIOUS  ARRANGEMENT  OF  THE 
SUCCESSION  IN  WHICH  SUBSTANCES  OUGHT  TO  BE 
ANALYZED. 

IT  is  not  a  matter  of  indifference  whether  the  student, 
in  analyzing  for  the  sake  of  practice,  follow  no  rule  or 
order  whatever  in  the  selection  of  substances  to  be  ex- 
amined, or  whether,  on  the  contrary,  his  investigations  and 
experiments  follow  a  definite  system.  Many  ways  may 
lead  to  the  desired  end,  but  one  of  them  invariably  will 
prove  the  shortest.  1  will,  therefore,  here  point  out  a  sys- 
tem'which  experience  has  shown  will  lead  safely  and 
rapidly  to  the  object  in  view. 

Let  the  student  take  one  hundred  compounds,  distributed 
according  to  the  following  scheme,  and  the  successful 
examination  of  these  will  be  amply  sufficient  to  enable 
him  to  attain  the  desired  degree  of  skill  in  practical  ana- 
lysis. When  analyzing  for  the  sake  of  practice  only,  the 
student  must  above  all  things  possess  the  means  of  verify- 
ing the  results  obtained  by  his  experiments.  The  com- 
pounds to  be  examined  ought,  therefore,  to  be  mixed  by  a 
friend  who  knows  their  exact  composition. 

A.  From  I  to  20. 

AQUEOUS  SOLUTIONS  OF  SIMPLE  SALTS  :  e.  g.  sulphate 
of  soda,  sulphate  of  lime,  chloride  of  copper,  &c.  ; — for  the 
acquisition  of  the  method  to  be  pursued  in  the  analysis  of 
substances  soluble  in  water,  and  which  contain  but  one 
base.  In  these  investigations  it  is  only  intended  to  ascer- 
tain which  base  is  present  in  the  fluid  under  examination, 
12 


278  APPENDIX  TO  PART  SECOND. 

without  regard  to  the  detection  of  the  acid ;  it  is  not  neces- 
sary to  prove  that  no  other  base  is  present,  besides  the  one 
detected. 

B.  From  21  to  50. 

SALTS,  &c.,  (CONTAINING  ONE  BASE  AND  ONE  ACID,)  IN  A 
SOLID  FORM,  as  powder :  e.  g.  carbonate  of  barytes,  borate 
of  soda,  phosphate  of  lime,  arsenious  acid,  chloride  of 
sodium,  tartar,  acetate  of  copper,  sulphate  of  barytes,  chlo- 
ride of  lead,  &c  J — to  learn  how  to  convert  a  solid  sub- 
stance to  a  state  which  admits  of  its  examination,  (solution, 
or  fluxing,)  how  to  detect  ONE  metallic  oxide,  even  though 
the  substance  under  examination  be  NOT  soluble  in  water, 
and  how  to  prove  the  presence  of  ONE  acid.  Base  and 
acid  must  be  detected  ;  it  is  not  necessary  to  prove  that 
no  other  constituents,  &c.  are  present. 

C.  From  51  to  70. 

AQUEOUS  OR  ACID  SOLUTIONS  OF  SEVERAL  BASES  ; — 
to  acquire  the  method  of  separating  and  distinguishing 
several  metallic  oxides.  It  is  necessary  to  prove  that  no 
other  bases  are  present  besides  those  detected.  No  regard 
is  paid  to  the  acids. 

I.  From  No.  51  to  60.     To  acquire  the  method  of  se- 
parating  the   metallic   oxides  into  the  principal  groups. 
The  solutions  contain,  therefore,  e.  g.  potash,  lime,  and 
lead  ; — copper,  iron,  and  arsenic ; — barytes,  antimony,  bis- 
muth, and  potash,  &c. 

II.  From  No.  61   to   70.     To  acquire  the  method  of 
detecting  side  by  side  the  individual  bases  belonging  to  the 
same  group.     The  solutions  contain,  e.  g.  potash,  soda, 
arid  ammonia ; — zinc,  manganese,  and   nickel ; — capper, 
mercury,  and  lead ; — antimony,  tin,  arsenic,  &c. 

D.  From  71  to  80. 
AQUEOUS  SOLUTIONS  CONTAINING  SEVERAL  ACIDS,  EITHER 

IN  THEIR    FREE  OR    IN   THEIR    COMBINED    STATE,    6.  g.    Sul- 

phuric  acid,  phosphoric  acid,  and  boracic  acid  ; — carbonic 
acid,  sulphuretted  hydrogen,  and  hydrocyanic  acid  j  tarta- 


APPENDIX  TO  PART  SECOND.  279 

ric  acid,  citric  acid,  and  malic  acid  ; — chlorine,  iodine,  and 
bromine ; — nitric  acid,  hydrochloric  acid,  and  oxalic  acid ; — 
to  acquire  the  method  of  detecting  several  acids  contained 
in  the  same  compound.  It  is  necessary  to  prove  that  no 
other  acids  are  present  besides  those  detected.  The  bases 
are  disregarded. 

E.  From  81  to  100. 

ALLOYS,  MINERALS,  AND  MIXED  SUBSTANCES  OF  EVERY 
DESCRIPTION  ; — for  further  practice,  and  to  prove  that  the 
student  has  attained  the  object  he  had  in  view  when  enter- 
ing upon  these  experimental  examinations.  All  the  con- 
stituents of  a  substance  under  examination  must  be 
detected  j  the  nature  of  the  substance  must  be  examined. 


II. 

TABLE 

OF   THE 

MORE  FREQUENTLY  OCCURRING  FORMS  AND 

COMBINATIONS  OF  THE  SUBSTANCES  CONSIDERED  IN 

THE 'PRESENT  WORK, 

WITH   ESPECIAL    REGARD   TO  THE   CLASSES   TO   WHICH   THEY  BELONG, 
ACCORDING  TO  THEIR  VARIOUS  DEGREES  OF  SOLUBILITY 

IN   WATEE,   IN   HYDROCHLORIC    ACID,   OR   IN   NITRIC  ACID. 


PRELIMINARY  REMARKS. 


THE  various  classes  to  which  compound  substances  be- 
long according  to  the  division  specified  at  §  106,  are  ex- 
pressed by  figures.  Thus  1  or  I  means  a  substance  solu- 
ble in  water  ;  2  or  II  a  substance  insoluble  in  water,  but 
soluble  in  hydrochloric  acid,  or  nitric  acid  ;  3  or  III  a  sub- 
stance insoluble  both  in  water  and  acids.  The  Roman 
figures  denote  officinal  and  more  frequently  occurring  com- 
pounds, whilst  the  Arabian  figures  indicate  less  frequently 
occurring  compounds.  For  those  substances  standing  as  it 
were,  on  the  limits  between  the  various  classes,  the  figures 
of  the  classes  in  question  are  jointly  expressed  :  thus  1 — 2 
signifies  a  substance  difficultly  soluble  in  water,  but  soluble 
in  hydrochloric  acid  or  nitric  acid  ;  1 — 3  a  body  difficultly 
soluble  in  water  and  the  solubility  of  which  is  not  increased 
by  the  addition  of  acids ;  and  2 — 3  a  substance  insoluble 
in  water  and  difficultly  soluble  in  hydrochloric  acid  and  in 
nitric  acid  ;  wherever  the  relation  of  a  substance  to  hydro- 


PRELIMINARY   REMARKS. 


281 


chloric  acid  is  different  from  that  to  nitric  acid,  this  is 
stated  in  the  notes. 

The  haloid  salts  and  sulphur  compounds  will  be  found 
in  the  columns  of  the  protoxide  and  peroxide-  Most  of 
the  salts  given  are  neutral,  the  basic  and  acid  and  double 
salts  are  mentioned  in  the  notes  j  the  small  figures  placed 
near  the  corresponding  neutral  or  simple  salts,  refer  to 
these.  Cyanogen,  chloric  acid,  citric  acid,  malic  acid, 
benzoic  acid,  succinic  acid,  and  formic  acid,  are  of  more 
frequent  occurrence  only  in  combination  with  a  few  bases, 
and  have,  therefore,  not  been  admitted  into  the  table.  The 
most  frequently  occurring  combinations  of  these  substances 
are  :  cyanide  of  potassium  I,  ferrocyanide  of  potassium  I, 
ferricyanide  of  potassium  I,  sesqui-ferrocyanide  of  potas- 
sium (Prussian  blue)  III,  ferrocyanide  of  zinc  and  potas- 
sium II — III,  chlorate  of  potash  I,  the  alkaline  citrates  I, 
the  alkaline  malates  I,  perraalate  of  iron  I,  the  alkaline  ben- 
zoates  I,  the  alkaline  succinates  I,  and  the  alkaline  for- 
miates  L 


2S2 


A  TABLE  OF  THE  VARIOUS  FORMS 


KO 

NaONH4  O 

BaO 

SrO 

CaO  MgO 

AlsOs 

MnO 

FeOFezOsCoONiO 

ZnO 

I 

t 

I 

1 

I-II 

II 

II 

II 

II 

n 

II 

n 

8 

I 

i 

I 

I 

I-II 

2 

II 

II 

n 

15 

16 

n 

Cl 

1 

112 

I 

I 

I 

] 

1 

I 

I 

Il2 

1 

I 

1 

J 

I 

1 

1 

1 

1 

1 

1 

1 

1 

1 

80s 

II 

113 

III 

m 

i-m 

I 

11-13 

I 

I 

I 

1 

1 

I 

NOs 

I 

1 

I 

i 

i 

1 

1 

I 

1 

1 

I 

I 

1 

POs 

1 

Iio 

110 

2 

2 

IIU 

2 

2 

2 

2 

n 

2 

2 

2 

C02 

12 

Iu 

II 

II 

n 

II 

II 

2 

2 

II 

CaOs 

13 

1 

2 

2 

ii 

2 

2 

2 

1-2 

1-2 

g 

2 

2 

BOa 

14 

14 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

A 

I 

I 

I 

1 

i 

1 

1 

1 

1 

1 

1 

J 

T 

14-9 

n 

14 

2 

2 

ii 

1-2 

1 

1-2 

1-2 

18 

1 

2 

As05 

I 

i 

2 

2 

2 

2 

2 

2 

2 

2 

2 

2 

3 

As  Oa 

I 

i 

2 

1 

2 

2 

2 

2 

Cr03 

I 

i 

2 

2 

1 

1 

2 

1 

1 

2 

1 

NOTES. 

1.  SULPHATE  of  potash  and  alumina  I. 

2.  Bicarbonate  of  potash  I. 

3.  Binoxalate  of  potash  I. 

4.  Tartarized  borax  I. 

5.  Bitartrate  of  potash  I. 

6.  Tartrate  of  potash  and  ammonia  I. 

7.  Tartrate  of  potash  and  soda  I. 

8.  Tartrate  of  potash  and  peroxide  of  iron  I. 

9.  Tartrate  of  antimony  and  potash  I. 

10.  Phosphate  of  soda^nd  ammonia  I. 

11.  Bicarbonate  of  soda  I. 

12.  Chloride  of  iron  and  ammonium  I. 

13.  Sulphate  of  ammonia  and  alumina  I. 

14.  Basic  phosphate  of  lime  II. 

15.  Sulphuret  of  cobalt  is   easily  decomposed  by  nitric 

acid,  but  very  difficultly  by  hydrochloric  acid. 
This  substance  is  not  officinal. 


283 


AND  COMBINATIONS  OF  BODIES. 


CdO 

PbO 

SnO 

SnO2 

BiO 

CuO 

HGaO 

HgO 

AgO 

PtO2 

AuOa 

SbOs 

Cre  03 

. 

2 

218 

2 

2&3 

2 

1122 

II 

n 

2 

2 

35 

n&in 

s 

2 

2 

20 

20 

2 

23 

III 

in 

30 

3 

1136 

CI 

1 

I-IH 

1 

1 

I 

124 

H-m 

188 

III 

132-33 

134 

137 

i 

J 

1 

n 

2 

ii 

II 

3 

S03 

I 

i 

1 

1 

1 

125 

1-2 

129 

i-m 

1 

2 

i 

NOs 

1 

i 

121 

I 

127 

I 

j 

1 

i 

POs 

2 

2 

2 

2 

2 

2 

2 

CO? 

2 

II 

2 

II 

2 

2 

2 

C203 

2 

II 

2 

2 

2 

2 

2 

2 

1-2 

1 

B03 

1-2 

2 

2 

2 

2 

1 

2 

2 

A 

1 

Il9 

1 

1 

1 

126 

1-2 

1 

I 

1 

1 

r 

1-2 

n 

1-2 

2 

1 

1-2 

2 

2 

138 

1 

AsOs 

2 

2 

2 

2 

2 

2 

2 

1 

As  O3 

2 

n 

2 

2 

2 

2 

CrOa 

ii-in 

2 

2 

2 

2 

1-2 

2 

2 

2 

16.  The  same  applies  to  sulphuret  of  nickel. 

17.  The  same  applies  to  sulphuret  of  zinc. 

18.  Minium  is  converted  by  hydrochloric  acid  into  chlo- 

ride of  lead,  by  nitric  acid  into  an  oxide  soluble  in 
an  excess  of  the  acid  and  into  brown  peroxide  of 
lead,  insoluble  in  nitric  acid. 

19.  Basic  acetate  of  lead  I. 

20.  Sulphuret  and  bisulphuret  of  tin  are  decomposed  and 

dissolved  by  hydrochloric  acid,  whilst  they  are 
converted  into  insoluble  oxides  by  nitric  acid  in 
excess.  Sublimed  bisulphuret  of  tin  dissolves 
only  in  aqua  regia. 

21.  Basic  nitrate  of  bismuth  II. 

22.  Ammoniacal  oxide  of  copper  I. 

23.  Sulphuret  of  copper  is  difficultly  decomposed  by  hy 

drochloric  acid,  but  with  facility  by  nitric  acid, 

24.  Chloride  of  copper  and  ammonium  1. 

25.  Sulphate  of  copper  and  ammonia  1. 

26.  Basic  acetate  of  copper,  soluble  partially  in  water,  and 

completely  in  acids. 


284  NOTES. 

27.  Basic  protonitrate  of  mercury  and  ammonia  II. 

28.  Basic  chloride  of  mercury  and  ammonium  II. 

29.  Basic  persulphate  of  mercury  II. 

30.  Sulphuret  of  silver  soluble  only  in  nitric  acid. 

31.  Sulphuret  of  platinum  is  not  affected  by  hydrochloric 

acid ;  boiling  nitric  acid  converts  it  into  a  soluble 
sulphate  of  platinum. 

32.  Chloride  of  platinum  and  potassium  1 — 3. 

33.  Chloride  of  platinum  and  ammonium  1 — 3. 

34.  Chloride  of  gold  and  sodium  I. 

35.  Oxide  of  antimony  soluble   in  hydrochloric  acid,  but 

not  in  nitric  acid. 

36.  Sulphuret  of  antimony  and  calcium  1 — 2. 

37.  Basic  chloride  of  antimony  II. 

38.  Tartrate  of  antimony  and  potash  I. 


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3n  jHcmufartttraf,  2lrt0,   cmb 

Edited  by  E.  A.  PARNELL, 

Author  of  "  Elements  of  Chemical  Analysis" ;  late  Assistant  Chemical 
Lecturer  in  the  Medical  School  of  St.  Thomas's  Hospital.  Illustrated 
with  numerous  Wood  Engravings,  and  Specimens  of  Dyed  and  Print- 
ed Cottons. 

The  object  of  this  work  is  to  present  a  faithful,  concise,  and  yet  comprehensive 
view  of  the  applications  of  Chemistry  in  the  Arts  and  Manufactures,  comprising  not 
only  a  description  of  the  various  manufacturing  processes  as  now  practised,  but  an, 
explanation  of  the  scientific  principles  on  which  they  depend. 

It  too  frequently  happens,  that  those  most  interested  in  this  subject  (the  manu- 
facturers themselves)  are  deterred  from  studying  the  principles  of  the  processes 
they  practise,  by  an  idea  that  more  time  and  thought  are  required  for  that  purpose 
than  they  can  command.  Masters  are,  consequently,  sometimes  placed  in  a  state. 
of  subjection  to  their  workmen,  who  are  themselves  often  the  slaves  of  a  blind 
attachment  to  a  disadvantageous  manipulation,  the  evils  of  which  would  be  imme- 
diately suggested  by  applying  the  most  obvious  principles  of  the  process. 

To  obviate  such  difficulty  is  the  intention  of  the  present  work,  which  is  addressed, 
in  the  first  place,  to  the  Artisan  and  Manufacturer ;  but,  being  divested  as  far  as 
possible  of  all  technical  terms,  it  is  hoped  the  work  will  also  be  adapted  to  the  re- 
quirements of  the  general  reader.  Its  plan  embraces  an  account  not  only  of  th© 
Chemical  Arts  and  Manufactures,  properly  so  called,  but  likewise  of  such  processes 
in  Domestic  Economy  as  are  dependent  on  Chemistry,  the  importance  of  which  is 
not  sufficient  to  raise  them  to  the  rank  of  distinct  arts  or  manufactures. 

It  is  not  intended  to  adopt  the  form  of  a  Methodical  Treatise,  or  that  of  a  Dictiona- 
ry, but  to  give  precedence  to  articles  on  such  subjects  as  are  most  important,  or  pos- 
sess peculiar  interest  at  the  time.  Each  article  or  treatise  will  be  complete  in  itself, 
so  that  the  book  will  form  a  series  of  essays  ;  and,  to  allow  the  introduction  of  sev- 
eral subjects,  the  length  of  each  article  will  not  exceed,  on  the  average,  four  or  five 
octavo  sheets. 

The  accounts  of  the  more  important  manufactures  will  include  historical  sketch- 
es of  their  progress,  with  their  recent  statistics  ;  and  the  British  modes  of  conduct" 
ing  the  various  processes  will,  in  general,  be  more  fully  treated  of  than  those  prac- 
tised on  the  Continent,  excellent  descriptions  of  which  have  already  appeared  in 
the  English  language..  The  editor  will  be  assisted  by  several  gentlemen  who  are, 
or  have  been,  personally  engaged  in  superintending  the  working  of  the  various  pro- 
cesses. 

Among  the  subjects  which  will  be  introduced  in  the  early  numbers,  are- 
Gas   Illumination — General  Principles  of  the  Arts  of  Dyeing  and  Calico  Print- 
ing— Manufacture  of  Sulphuric  Acid — Indigo — Coffee,   Tea,  and 
Chocolate — Caoutchouc,  Borax,  Preservation  of  Wood, 
Zinc — Bichromate  of  Potash. 

The  articles  on  Dyeing  and  Calico  printing,  and  Dyeing  Materials,  will  be  illus- 
trated with  specimens  of  Dyed  and  Printed  Cottons,  and  those  on  Pigments,  when 
practicable  and  necessary,  with  examples  of  the  tints  of  such  as  are  not  commonly 
known. 

IT  The  work  will  be  continued  in  Monthly  Numbers,  Price  12*  each; 


A  8  Hydraulics,  Mechanics,  Steam-Engine,  $*c. 

HYDRAULICS    AND    MECHANICS. 

A.  Descriptive  and  Historical  Account  of  Hydraulic  and  other  Machines  for  Raising  Water,  including 
the  Steam  and  Fire  Engines,  ancient  and  modern  ;  with  Observations  on  various  subjects  connected 
with  the  Mechanic  Arts  ;    including  the  Progressive  Development  of  the  Steam  Engine  •  Descrip- 
tions of  every  variety  of  Bellows,  Piston,  and  Rotary  Pumps,  Fire  Engines,  Water  Rams,  Pressure 
Engines,  Air  Machines,  Eolipiles,  &c.     Remarks  on  Ancient  Wells,  Air  Beds,  Cog  Wheels,  Blow- 
pipes, Bellows  of  various  People,  Magic  Goblets,  Steam  Idols,  and  other  Machinery  of  Ancient  Tern* 
i    pies.    To  which  are  added  Experiments  on  Blowing  and  Spouting  Tubes,  and  other  original  De- 
'    vices,  Nature's  modes  and  Machinery  for  Raising  Water.      Historical  notices  respecting  Siphons, 
Fountains,  Water  Organs,  Clopsydrse,  Pipes,  Valves,  Cocks,  &c.     In  five  books.     Illustrated  by 
•    nearly  three  hundred  Engravings.    By  THOMAS  EVVBANK.     One  handsomely  printed  volume  of 
six  hundred  pages.    $3  50 

Although  the  subject  of  this  work  may  present  nothing  alluring  to  the  general  reader,  it  will  be  found  not  destitute  of 
interest  to  the  philosopher  and  intelligent  mechanic.  The  art  of  raising  water  has  ever  been  closely  connected  with  the 
progress  of  man  in  civilization,  so  much  so,  indeed,  that  the  state  of  this  art  among  a  people  may  be  taken  as  an  index  of 
their  position  on  the  scale  of  refinement.  It  is  also  an  art,  which,  from  its  importance,  called  forth  the  ingenuity  of  man 
in  the  infancy  of  society,  nor  is  it  improbable  that  itoriginated  some  of  the  simple  machines  of  mechanic  powers  them- 

It  was  a  favourite  subject  of  research  with  eminent  mathematicians  and  engineers  of  old,  and  the  labour  of  their  suc- 
cessors in  modern  flays,  have  been  rewarded  with  the  most  valuable  machine  which  the  arts  ever  presented  to  man,  the 
STEAM  ENGINE,  for  it  was  "raising  of  water,"  that  exercised  the  ingenuity  of  Decatus  and  Worcester,  Morland  and 
Papin,  Sa vary  and  Newcomen,  and  those  illustrious  men  whose  successive  labours  developed  and  matured  thai 
"  semi-omnipotent  engine,"  which  "  draweth  up  water  by  fire."  A  machine  that  has  already  changed  and  immeasura- 
bly improved  the  state  of  civil  society,  and  one  which,  in  conjunction  with  the  printing  press,  is  destined  to  renovate  both 
the  political  and  the  moral  world.  The  subject  is  therefore  intimately  connected  with  the  present  advanced  state  of  the 
arts ;  and  the  amazing  progress  made  in  them  during  the  last  two  centuries  may  be  attributed  in  some  degree  to  its  culti- 
vation.-'-Fide  Preface. 

"  This  work  of  Mr.  K wbank  seems  to  be  something  new  in  its  design,  which  M  effected  with  wonderful  ability  an!  success 
It  could  only  have  been  written  by  one,  a  large  portion  of  whose  life  had  been  spent  in  searching  the  dusty  volumes  of  an 
tiquity,  and  who  possessed  besides  an  ardent  enthusiasm  in  the  cause  of  science  and  mechanic  improvement.  We  have 
not  time  to  give  anything  like  a  general  summary  of  its  contents.  It  traces  (he  history  of  machinery  of  all  sorts  from  the 
very  earliest  dawn  of  its  invention — exploring  wi'th  the  most  ceaseless  assiduity  the  records  of  antiquity,  and  cross  exam- 
ining their  traditions,  customs,  &,c.  with  consummate  skill,  intermingling  the  whole  with  the  most  entertaining  sketches 
of  life  and  character  and  the  most  just  and  instructive  reflections  upon  the  features  of  society  and  ordinary  lite,  which  are 
indicated  by  the  habits  thus  brought  to  light.  The  work  is  divided  into  five  books,  of  which  the  general  subjects  are  at 
follows:  1.  Primitive  and  Ancient  Devices  for  Raising  Water :  2.  Machines  for  Raising  Water  by  the  Pressure  of  the 
Atmosphere:  3.  Machines  for  Raising  Water  by  Compressure  independently  of  Atmospheric  influence  :  4.  Machines  for 
Raising  Water,  chiefly  of  Modern  Origin,  including  early  modern  applications  of  steam  for  that  purpose  :  5.  Novel  De- 
vices for  Raising  Water,  with  an  account  of  syphons,  locks,  valves,  cfopsydia,  &c.  It  is  illustrated  by  nearly  300  fine  en- 
gravings, and  is  published  in  the  finest  style  of  the  typographic  art. —  Tribune." 

"  This  is  a  highly  valuable  production,  replete  with  novelty  and  interest,  and  adapted  to  gratify  equally  the  historian, 
the  philosopher  and  tne  mechanician,  being  the  result  of  a  protracted  and  extensive  research  among  the  arcana  of  histori- 
al  and  scientific  literature."— National  Intelligencer. 

HODGE    ON    THE    STEAM-ENGINE. 

The  Steam  Engine,  its  Origin  and  Gradual  Improvement,  from  the  time  of  Hero  to  the  present  day, 
as  adapted  to  Manufactures,  Locomotion  and  Navigation.  Illustrated  with  forty-eight  plates  in  full 
detail,  numerous  wood  cuts,  &c.  by  Paul  R.  Hodge,  C.E.  1  vol.  folio  of  plt-tes,  and  letter-press  in 
8vo.  $10  00. 

"  The  letter-press  volume  furnishes  a  comprehensive  history  of  the  invention  and  the  various  im- 
provements which  have  been  made  in  the  steam-engine,  from  the  earliest  period  to  the  present  time, 
together  with  such  practical  rules  and  explanations  as  are  necessary  to  enable  the  mechanic  to  design 
and  construct  a  machine  of  any  required  power,  and  of  the  most  improved  form,  for  any  of  the  numer- 
ous applications  of  steam.  For  the  purpose  of  rendering  the  reference  from  the  letter-press  to  the 
plates  more  convenient,  the  engraved  illustrations  are  published  in  a  separate  volume,  in  the  folio 
form.  These  plates  are  all  drawn  to  certain  scales,  and  the  dimensions  of  every  part  may  be  taken, 
and  machines  built  from  any  of  the  designs. 

"  The  most  recent  and  approved  engines  of  their  respective  classes  appear  to  have  been  selected, 
and,  with  four  exceptions  only,  are  all  of  American  construction  and  arrangement.  The  volume  of 
plates,  as  a  work  of  the  art  of  drawing,  forms  one  of  the  most  splendid  specimens  that  has  ever  fallen 
under  our  observation.  Mr.  Hodge,  the  author  of  this  truly  practical  and  valuable  work,  is,  it  will  be 
recollected,  the  inventor  of  the  steam  fire-engine,  the  utility  of  which,  in  extinguishing  fires,  has  been 
fully  tested." — Courier  <J-  Enquirer. 

LAFEVER'S    MODERN    ARCHITECTURE. 

Beauties  of  Modern  Architecture  :  consisting  of  forty-eight  plates  of  Original  Designs,  with  Plans, 
Elevations  and  Sections,  also  a  Dictionary  of  Technical  Terms  ;  the  whole  forming  a  complete 
Manual  for  the  Practical  Builder.  By  M.  Lafever,  Architect.  1  vol.  large  8vo.  half  bound.  $6  00 

LAFEVER'S    STAIR-CASE    AND    HAND-RAIL    CONSTRUCTION. 

The  Modern  Practice  of  Stair-case  and  Hand-rail  Construction,  practically  explained,  in  a  series  «f 
Designs.    By  M.  Lafever,  Architect.    With  Plans  and  Elevations  for  Ornamental  Villa*.    Fift««a 
Plates.    I  vol.  large  8vo.    $300. 
•Tlu  works  of  Lafever  are  pronounced  by  the  practical  man  to  be  the  most  useful  ever  published. 


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